Hello,

Thank you for your question. Please check following things:

1. Duplicate the receipt, change date to same as the original, set received value to same sum as original record but negative and try to save.

2. If you are using different currency from base currency on prepayment then please check that you have imported exchange rates correctly for the date you are trying to enter.

3. Have you activated "Use Prepayments, not On Account" and "Force Unique Prepayment Number" activated in SL>>Settings>>Account Usage S/L?

Best Regards,
Rasmus