1. Click Suppliers, click the required supplier then click Activity.
2. Click the payment you want to unallocate, click Unallocate or Unallocate transaction, then click Yes.
   
   If the option is disabled, check that you have access to the 'Unallocate payment' option in Settings, User Management, if you have access, check why you can't unallocate a transaction.

[BCB:19:UK - Sales message :ECB]