Suggestions:
System shows the message when one more Sales return is already saved for a single invoice. System will show ‘VTSRAINV’, ‘Full Not allowed’, ‘Already another Sales Return Done against this invoice, full return cannot be done’. Users will have to check the invoice used in Sales returns previous transactions. If the previous Sales return is not confirmed then the user can delete the line item and remove the invoice id from the header. This will enable the user to make a full return if required for the new record.