Hi,
Please check G/Ls are configured in OBYY
Path --- IMG --> Financial Accounting (New) --> Financial Accounting Global Settings (New) --> Tax on Sales/Purchases --> Posting --> Define Account for Exchange Rate Difference Posting
OR
In case you are using Contract Accounts Receivable and Payable check whether you have assigned G/Ls exchange rate.
Hope, this solves your issue.
Regards,
Tejas