Hi,I'm facing the same issue that you mentioned above while integrating AEM 6.3 and ACS(on-premise). Can you please specify which Authorization value to be added in dispatcher.Thank You!

polizzigaetano-codeland​ i found the same error even after doing everything mentioned. can you please let me know authorization value you added for the integration to work.should i white-list something.Thank You!

This issue has been solved after the AEM author instance port has been removed from External accounts configuration.