diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 1cd0a1121..d0a54ad9f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -23,6 +23,7 @@ jobs:
       WCRS_USE_XVFB_FOR_WICKEDPDF: true
       ENV_VARIABLE_TEST_FEATURE: true
       WCRS_GOVPAY_CALLBACK_WEBHOOK_SIGNING_SECRET: foo
+      WCRS_GOVPAY_BACK_OFFICE_CALLBACK_WEBHOOK_SIGNING_SECRET: foo2
 
     steps:
       # Downloads a copy of the code in your repository before running CI tests
diff --git a/app/services/waste_carriers_engine/govpay_payment_webhook_signature_service.rb b/app/services/waste_carriers_engine/govpay_payment_webhook_signature_service.rb
index 18305fcfe..8bc28e831 100644
--- a/app/services/waste_carriers_engine/govpay_payment_webhook_signature_service.rb
+++ b/app/services/waste_carriers_engine/govpay_payment_webhook_signature_service.rb
@@ -5,22 +5,33 @@ class GovpayPaymentWebhookSignatureService < BaseService
     class DigestFailure < StandardError; end
 
     def run(body:)
-      hmac_digest(body.to_s)
+      generate_signatures(body.to_s)
     rescue StandardError => e
       Rails.logger.error "Govpay payment webhook signature generation failed: #{e}"
-      Airbrake.notify(e, body:, signature:)
+      Airbrake.notify(e, body:)
       raise DigestFailure, e
     end
 
     private
 
-    def webhook_signing_secret
-      @webhook_signing_secret = ENV.fetch("WCRS_GOVPAY_CALLBACK_WEBHOOK_SIGNING_SECRET")
+    def generate_signatures(body)
+      {
+        front_office: hmac_digest(body, front_office_secret),
+        back_office: hmac_digest(body, back_office_secret)
+      }
     end
 
-    def hmac_digest(body)
+    def front_office_secret
+      ENV.fetch("WCRS_GOVPAY_CALLBACK_WEBHOOK_SIGNING_SECRET")
+    end
+
+    def back_office_secret
+      ENV.fetch("WCRS_GOVPAY_BACK_OFFICE_CALLBACK_WEBHOOK_SIGNING_SECRET")
+    end
+
+    def hmac_digest(body, secret)
       digest = OpenSSL::Digest.new("sha256")
-      OpenSSL::HMAC.hexdigest(digest, webhook_signing_secret, body)
+      OpenSSL::HMAC.hexdigest(digest, secret, body)
     end
   end
 end
diff --git a/app/services/waste_carriers_engine/validate_govpay_payment_webhook_body_service.rb b/app/services/waste_carriers_engine/validate_govpay_payment_webhook_body_service.rb
index a40ee4e03..e6ebffbf0 100644
--- a/app/services/waste_carriers_engine/validate_govpay_payment_webhook_body_service.rb
+++ b/app/services/waste_carriers_engine/validate_govpay_payment_webhook_body_service.rb
@@ -7,8 +7,9 @@ class ValidationFailure < StandardError; end
     def run(body:, signature:)
       raise ValidationFailure, "Missing expected signature" if signature.blank?
 
-      body_signature = GovpayPaymentWebhookSignatureService.run(body:)
-      return true if body_signature == signature
+      body_signatures = GovpayPaymentWebhookSignatureService.run(body:)
+
+      return true if body_signatures[:front_office] == signature || body_signatures[:back_office] == signature
 
       raise ValidationFailure, "digest/signature header mismatch"
     end
diff --git a/spec/services/waste_carriers_engine/govpay_payment_webhook_signature_service_spec.rb b/spec/services/waste_carriers_engine/govpay_payment_webhook_signature_service_spec.rb
index e75b5dab4..2664f83e1 100644
--- a/spec/services/waste_carriers_engine/govpay_payment_webhook_signature_service_spec.rb
+++ b/spec/services/waste_carriers_engine/govpay_payment_webhook_signature_service_spec.rb
@@ -5,8 +5,8 @@
 module WasteCarriersEngine
   RSpec.describe GovpayPaymentWebhookSignatureService do
     describe ".run" do
-
-      let(:webhook_signing_secret) { ENV.fetch("WCRS_GOVPAY_CALLBACK_WEBHOOK_SIGNING_SECRET") }
+      let(:front_office_secret) { ENV.fetch("WCRS_GOVPAY_CALLBACK_WEBHOOK_SIGNING_SECRET") }
+      let(:back_office_secret) { ENV.fetch("WCRS_GOVPAY_BACK_OFFICE_CALLBACK_WEBHOOK_SIGNING_SECRET") }
       let(:digest) { OpenSSL::Digest.new("sha256") }
 
       subject(:run_service) { described_class.run(body: webhook_body) }
@@ -27,13 +27,17 @@ module WasteCarriersEngine
 
       context "with a complete webhook body" do
         let(:webhook_body) { JSON.parse(file_fixture("govpay/webhook_payment_update_body.json").read).to_s }
-        let(:valid_signature) { OpenSSL::HMAC.hexdigest(digest, webhook_signing_secret, webhook_body) }
+        let(:valid_front_office_signature) { OpenSSL::HMAC.hexdigest(digest, front_office_secret, webhook_body) }
+        let(:valid_back_office_signature) { OpenSSL::HMAC.hexdigest(digest, back_office_secret, webhook_body) }
 
-        it { expect(run_service).to eq valid_signature }
+        it "returns correct signatures for both front office and back office" do
+          result = run_service
+          expect(result[:front_office]).to eq valid_front_office_signature
+          expect(result[:back_office]).to eq valid_back_office_signature
+        end
 
         it "does not report an error" do
           run_service
-
           expect(Airbrake).not_to have_received(:notify)
         end
       end
diff --git a/spec/services/waste_carriers_engine/validate_govpay_payment_webhook_body_service_spec.rb b/spec/services/waste_carriers_engine/validate_govpay_payment_webhook_body_service_spec.rb
index 24271de62..09c3b76da 100644
--- a/spec/services/waste_carriers_engine/validate_govpay_payment_webhook_body_service_spec.rb
+++ b/spec/services/waste_carriers_engine/validate_govpay_payment_webhook_body_service_spec.rb
@@ -5,20 +5,20 @@
 module WasteCarriersEngine
   RSpec.describe ValidateGovpayPaymentWebhookBodyService do
     describe ".run" do
-
-      let(:headers) { "Pay-Signature" => signature }
       let(:webhook_body) { JSON.parse(file_fixture("govpay/webhook_payment_update_body.json").read).to_s }
-      let(:webhook_signing_secret) { ENV.fetch("WCRS_GOVPAY_CALLBACK_WEBHOOK_SIGNING_SECRET") }
-      let(:digest) { OpenSSL::Digest.new("sha256") }
-      let(:valid_signature) { Faker::Number.hexadecimal(digits: 20) }
+      let(:valid_front_office_signature) { Faker::Number.hexadecimal(digits: 20) }
+      let(:valid_back_office_signature) { Faker::Number.hexadecimal(digits: 20) }
       let(:signature_service) { instance_double(GovpayPaymentWebhookSignatureService) }
       let(:signature) { nil }
 
-      subject(:run_service) { described_class.run(body: webhook_body, signature:) }
+      subject(:run_service) { described_class.run(body: webhook_body, signature: signature) }
 
       before do
         allow(GovpayPaymentWebhookSignatureService).to receive(:new).and_return(signature_service)
-        allow(signature_service).to receive(:run).and_return(valid_signature)
+        allow(signature_service).to receive(:run).and_return(
+          front_office: valid_front_office_signature,
+          back_office: valid_back_office_signature
+        )
         allow(Airbrake).to receive(:notify)
       end
 
@@ -29,7 +29,6 @@ module WasteCarriersEngine
 
         it "logs an error" do
           run_service
-
           expect(Airbrake).to have_received(:notify)
         rescue ValidateGovpayPaymentWebhookBodyService::ValidationFailure
           # we expect the service to raise an exception as well as logging the error.
@@ -48,14 +47,24 @@ module WasteCarriersEngine
         it_behaves_like "fails validation"
       end
 
-      context "with a valid signature" do
-        let(:signature) { valid_signature }
+      context "with a valid front office signature" do
+        let(:signature) { valid_front_office_signature }
 
         it { expect(run_service).to be true }
 
         it "does not report an error" do
           run_service
+          expect(Airbrake).not_to have_received(:notify)
+        end
+      end
 
+      context "with a valid back office signature" do
+        let(:signature) { valid_back_office_signature }
+
+        it { expect(run_service).to be true }
+
+        it "does not report an error" do
+          run_service
           expect(Airbrake).not_to have_received(:notify)
         end
       end