diff --git a/setup.py b/setup.py
index fbc963e2..64217ac0 100644
--- a/setup.py
+++ b/setup.py
@@ -78,6 +78,11 @@ def run(self):
                 " await self.files_getUploadURLExternal(",
                 async_source,
             )
+            async_source = re.sub(
+                r" self._upload_file\(",
+                " await self._upload_file(",
+                async_source,
+            )
             async_source = re.sub(
                 r" self.files_completeUploadExternal\(",
                 " await self.files_completeUploadExternal(",
diff --git a/slack_sdk/web/async_base_client.py b/slack_sdk/web/async_base_client.py
index ffdb8b69..a33f287c 100644
--- a/slack_sdk/web/async_base_client.py
+++ b/slack_sdk/web/async_base_client.py
@@ -11,6 +11,7 @@
 )  # type: ignore
 from .async_slack_response import AsyncSlackResponse
 from .deprecation import show_deprecation_warning_if_any
+from .file_upload_v2_result import FileUploadV2Result
 from .internal_utils import (
     convert_bool_to_0_or_1,
     _build_req_args,
@@ -214,3 +215,28 @@ async def _request(self, *, http_verb, api_url, req_args) -> Dict[str, Any]:
             req_args=req_args,
             retry_handlers=self.retry_handlers,
         )
+
+    async def _upload_file(
+        self,
+        *,
+        url: str,
+        data: bytes,
+        logger: logging.Logger,
+        timeout: int,
+        proxy: Optional[str],
+        ssl: Optional[SSLContext],
+    ) -> FileUploadV2Result:
+        """Upload a file using the issued upload URL"""
+        result = await _request_with_session(
+            current_session=self.session,
+            timeout=timeout,
+            logger=logger,
+            http_verb="POST",
+            api_url=url,
+            req_args={"data": data, "proxy": proxy, "ssl": ssl},
+            retry_handlers=self.retry_handlers,
+        )
+        return FileUploadV2Result(
+            status=result.get("status_code"),
+            body=result.get("body"),
+        )
diff --git a/slack_sdk/web/async_client.py b/slack_sdk/web/async_client.py
index 2c8b90e8..4fcf7bb9 100644
--- a/slack_sdk/web/async_client.py
+++ b/slack_sdk/web/async_client.py
@@ -23,7 +23,6 @@
     _warn_if_text_or_attachment_fallback_is_missing,
     _remove_none_values,
     _to_v2_file_upload_item,
-    _upload_file_via_v2_url,
     _validate_for_legacy_client,
     _print_files_upload_v2_suggestion,
 )
@@ -3584,7 +3583,7 @@ async def files_upload_v2(
 
         # step2: "https://files.slack.com/upload/v1/..." per file
         for f in files:
-            upload_result = _upload_file_via_v2_url(
+            upload_result = await self._upload_file(
                 url=f["upload_url"],
                 data=f["data"],
                 logger=self._logger,
@@ -3592,9 +3591,9 @@ async def files_upload_v2(
                 proxy=self.proxy,
                 ssl=self.ssl,
             )
-            if upload_result.get("status") != 200:
-                status = upload_result.get("status")
-                body = upload_result.get("body")
+            if upload_result.status != 200:
+                status = upload_result.status
+                body = upload_result.body
                 message = (
                     "Failed to upload a file "
                     f"(status: {status}, body: {body}, filename: {f.get('filename')}, title: {f.get('title')})"
diff --git a/slack_sdk/web/async_internal_utils.py b/slack_sdk/web/async_internal_utils.py
index 6c4c025a..b5b308d4 100644
--- a/slack_sdk/web/async_internal_utils.py
+++ b/slack_sdk/web/async_internal_utils.py
@@ -108,7 +108,7 @@ def convert_params(values: dict) -> dict:
 
             try:
                 async with session.request(http_verb, api_url, **req_args) as res:
-                    data: Union[dict, bytes] = {}
+                    data: Union[dict, bytes, str] = {}
                     if res.content_type == "application/gzip":
                         # admin.analytics.getFile
                         data = await res.read()
@@ -117,6 +117,14 @@ def convert_params(values: dict) -> dict:
                             headers=res.headers,
                             data=data,
                         )
+                    elif res.content_type == "text/plain":
+                        # https://files.slack.com/upload/v1/...
+                        data = await res.text()
+                        retry_response = RetryHttpResponse(
+                            status_code=res.status,
+                            headers=res.headers,
+                            data=data,
+                        )
                     else:
                         try:
                             data = await res.json()
@@ -143,7 +151,9 @@ def convert_params(values: dict) -> dict:
                                 )
 
                     if logger.level <= logging.DEBUG:
-                        body = data if isinstance(data, dict) else "(binary)"
+                        body = "(binary)"
+                        if isinstance(data, dict) or isinstance(data, str):
+                            body = data
                         logger.debug(
                             "Received the following response - "
                             f"status: {res.status}, "
diff --git a/slack_sdk/web/base_client.py b/slack_sdk/web/base_client.py
index 5bef2876..4c24fa3f 100644
--- a/slack_sdk/web/base_client.py
+++ b/slack_sdk/web/base_client.py
@@ -21,12 +21,14 @@
 
 from slack_sdk.errors import SlackRequestError
 from .deprecation import show_deprecation_warning_if_any
+from .file_upload_v2_result import FileUploadV2Result
 from .internal_utils import (
     convert_bool_to_0_or_1,
     get_user_agent,
     _get_url,
     _build_req_args,
     _build_unexpected_body_error_message,
+    _upload_file_via_v2_url,
 )
 from .slack_response import SlackResponse
 from slack_sdk.http_retry import default_retry_handlers
@@ -560,10 +562,34 @@ def _build_urllib_request_headers(
         if has_json:
             headers.update({"Content-Type": "application/json;charset=utf-8"})
         if has_files:
-            # will be set afterwards
+            # will be set afterward
             headers.pop("Content-Type", None)
         return headers
 
+    def _upload_file(
+        self,
+        *,
+        url: str,
+        data: bytes,
+        logger: logging.Logger,
+        timeout: int,
+        proxy: Optional[str],
+        ssl: Optional[SSLContext],
+    ) -> FileUploadV2Result:
+        """Upload a file using the issued upload URL"""
+        result = _upload_file_via_v2_url(
+            url=url,
+            data=data,
+            logger=logger,
+            timeout=timeout,
+            proxy=proxy,
+            ssl=ssl,
+        )
+        return FileUploadV2Result(
+            status=result.get("status"),
+            body=result.get("body"),
+        )
+
     # =================================================================
 
     @staticmethod
diff --git a/slack_sdk/web/client.py b/slack_sdk/web/client.py
index 18c8a9c2..074dca03 100644
--- a/slack_sdk/web/client.py
+++ b/slack_sdk/web/client.py
@@ -14,7 +14,6 @@
     _warn_if_text_or_attachment_fallback_is_missing,
     _remove_none_values,
     _to_v2_file_upload_item,
-    _upload_file_via_v2_url,
     _validate_for_legacy_client,
     _print_files_upload_v2_suggestion,
 )
@@ -3575,7 +3574,7 @@ def files_upload_v2(
 
         # step2: "https://files.slack.com/upload/v1/..." per file
         for f in files:
-            upload_result = _upload_file_via_v2_url(
+            upload_result = self._upload_file(
                 url=f["upload_url"],
                 data=f["data"],
                 logger=self._logger,
@@ -3583,9 +3582,9 @@ def files_upload_v2(
                 proxy=self.proxy,
                 ssl=self.ssl,
             )
-            if upload_result.get("status") != 200:
-                status = upload_result.get("status")
-                body = upload_result.get("body")
+            if upload_result.status != 200:
+                status = upload_result.status
+                body = upload_result.body
                 message = (
                     "Failed to upload a file "
                     f"(status: {status}, body: {body}, filename: {f.get('filename')}, title: {f.get('title')})"
diff --git a/slack_sdk/web/file_upload_v2_result.py b/slack_sdk/web/file_upload_v2_result.py
new file mode 100644
index 00000000..abacca44
--- /dev/null
+++ b/slack_sdk/web/file_upload_v2_result.py
@@ -0,0 +1,7 @@
+class FileUploadV2Result:
+    status: int
+    body: str
+
+    def __init__(self, status: int, body: str):
+        self.status = status
+        self.body = body
diff --git a/slack_sdk/web/internal_utils.py b/slack_sdk/web/internal_utils.py
index c7d14562..98cad3cc 100644
--- a/slack_sdk/web/internal_utils.py
+++ b/slack_sdk/web/internal_utils.py
@@ -377,6 +377,9 @@ def _upload_file_via_v2_url(
         else:
             raise SlackRequestError(f"Invalid proxy detected: {proxy} must be a str value")
 
+    if logger.level <= logging.DEBUG:
+        logger.debug(f"Sending a request: POST {url}")
+
     resp: Optional[HTTPResponse] = None
     req: Request = Request(method="POST", url=url, data=data, headers={})
     if opener:
@@ -388,8 +391,10 @@ def _upload_file_via_v2_url(
     body: str = resp.read().decode(charset)  # read the response body here
     if logger.level <= logging.DEBUG:
         message = (
-            "Received the following response - ",
-            f"status: {resp.status}, " f"headers: {dict(resp.headers)}, " f"body: {body}",
+            "Received the following response - "
+            f"status: {resp.status}, "
+            f"headers: {dict(resp.headers)}, "
+            f"body: {body}"
         )
         logger.debug(message)
 
diff --git a/slack_sdk/web/legacy_base_client.py b/slack_sdk/web/legacy_base_client.py
index 6da969ab..1efd2644 100644
--- a/slack_sdk/web/legacy_base_client.py
+++ b/slack_sdk/web/legacy_base_client.py
@@ -26,12 +26,14 @@
 from slack_sdk.errors import SlackRequestError
 from .async_internal_utils import _files_to_data, _get_event_loop, _request_with_session
 from .deprecation import show_deprecation_warning_if_any
+from .file_upload_v2_result import FileUploadV2Result
 from .internal_utils import (
     convert_bool_to_0_or_1,
     get_user_agent,
     _get_url,
     _build_req_args,
     _build_unexpected_body_error_message,
+    _upload_file_via_v2_url,
 )
 from .legacy_slack_response import LegacySlackResponse as SlackResponse
 from ..proxy_env_variable_loader import load_http_proxy_from_env
@@ -521,10 +523,33 @@ def _build_urllib_request_headers(
         if has_json:
             headers.update({"Content-Type": "application/json;charset=utf-8"})
         if has_files:
-            # will be set afterwards
+            # will be set afterward
             headers.pop("Content-Type", None)
         return headers
 
+    def _upload_file(
+        self,
+        *,
+        url: str,
+        data: bytes,
+        logger: logging.Logger,
+        timeout: int,
+        proxy: Optional[str],
+        ssl: Optional[SSLContext],
+    ) -> FileUploadV2Result:
+        result = _upload_file_via_v2_url(
+            url=url,
+            data=data,
+            logger=logger,
+            timeout=timeout,
+            proxy=proxy,
+            ssl=ssl,
+        )
+        return FileUploadV2Result(
+            status=result.get("status"),
+            body=result.get("body"),
+        )
+
     # =================================================================
 
     @staticmethod
diff --git a/slack_sdk/web/legacy_client.py b/slack_sdk/web/legacy_client.py
index c3d11975..78c5d0fd 100644
--- a/slack_sdk/web/legacy_client.py
+++ b/slack_sdk/web/legacy_client.py
@@ -25,7 +25,6 @@
     _warn_if_text_or_attachment_fallback_is_missing,
     _remove_none_values,
     _to_v2_file_upload_item,
-    _upload_file_via_v2_url,
     _validate_for_legacy_client,
     _print_files_upload_v2_suggestion,
 )
@@ -3586,7 +3585,7 @@ def files_upload_v2(
 
         # step2: "https://files.slack.com/upload/v1/..." per file
         for f in files:
-            upload_result = _upload_file_via_v2_url(
+            upload_result = self._upload_file(
                 url=f["upload_url"],
                 data=f["data"],
                 logger=self._logger,
@@ -3594,9 +3593,9 @@ def files_upload_v2(
                 proxy=self.proxy,
                 ssl=self.ssl,
             )
-            if upload_result.get("status") != 200:
-                status = upload_result.get("status")
-                body = upload_result.get("body")
+            if upload_result.status != 200:
+                status = upload_result.status
+                body = upload_result.body
                 message = (
                     "Failed to upload a file "
                     f"(status: {status}, body: {body}, filename: {f.get('filename')}, title: {f.get('title')})"