diff --git a/src/NotchPay.php b/src/NotchPay.php
index d462b6e..0a7bc8d 100644
--- a/src/NotchPay.php
+++ b/src/NotchPay.php
@@ -39,7 +39,7 @@ private static function validateApiKey($apiKey): bool
             throw new InvalidArgumentException('Api key must be a string and cannot be empty');
         }
 
-        if(substr( $apiKey, 0, 2 ) !== "b." && substr( $apiKey, 0, 3 ) !== "sb."  && substr( $apiKey, 0, 2 ) !== "pk.") {
+        if(substr( $apiKey, 0, 2 ) !== "b." && substr( $apiKey, 0, 3 ) !== "sb."  && substr( $apiKey, 0, 3 ) !== "pk.") {
             throw new InvalidArgumentException('Api key must have a valid signature.');
         }
         return true;