Dear Sangeetha,
When you click on Document ID, synchronous call would be triggered from COD to External system (ERP/CRM).
You can check the error details if you have access to COD backend.
Or
Check in SRT_UTIL t-code in ERP system, here you need to check whether the request and response message are triggering from ERP system.
You can past the error message to investigate the issue further.
Thanks & Regards
Praveen Kumar
SAP Product Support