Hi Said.
If you want to keep the same payment lot, then you can use the post online functionaly and post the item into the bank clearing account:
- start FP05, enter the payment lot ID, display it, select the item you want to clarify and choose "clarify"
- select option "post online"
- the false item should be visible in the view - now enter another item with all the same data, except for the negative amount
- post it
In general, I dont think you can remove an item from payment lot after its being posted. Another possibility is reversing the reconciliation key for that payment lot (using FP08M), and using another posting lot without the payment entered by mistake.
Marko