If the debt is written off in Bee Free as a bad debt, you cant really reverse this easily.
The complicated way is:
-go to the clients financial activity
-delete the zero payment just above the write off (hover over it and click the 'X'
- click on the invoice number that is labeled write off
- this takes you to the consult screen, untick the 'ready to pay'
- delete any invoice lines so that the invoice is blank
- save it
- go to collect payments screen - the old written off invoice will be there
The easier way to do this is to create a new invoice of the same value and pay that off.