i face same issue file activating MPOS with customization. this is one warning i have in event viewer :
1. AzureActiveDirectoryUserAuthenticationProvider.acquireTokenWithParam skipped accessing current user's information because corresponding data structure was not initialized.
2. DeviceAuthenticationProvider.acquireToken did not find a device token in the application stroage.
3. Server response status code is '401'.
4. Unauthorized response with error: The audience validation failed.. ErrorResourceId: Microsoft_Dynamics_Commerce_Runtime_InvalidAudience with Correlation Id:
5. The Retail Server Request with request id '-------------' and request url '--------------/Commerce/ActivateDevice?api-version=7.3' failed. Error: The audience validation failed., Status code 401.
6.Chained request execution failed.
7.Device Activation failed. Errors=[{"errorCode":"Microsoft_Dynamics_Commerce_Runtime_InvalidAudience","message":"The audience validation failed. Contact your system administrator to set up identity providers properly in retail headquarters.\r\n- If you are using Personnel ID and Password logon, make sure relying parties are correctly configured.\r\n- If you are using Azure AD logon, make sure both relying parties and server resource ids are correctly configured."}];
(Made sure AADClientId and AADRetailServerResourceId in DllHost.exe file is same as in the HQ parameter relying party and server resource id. )
8. The device activation operation failed.