Hi, the custom cloud
Move to the relevant invoice and edit the invoice to include a new item called Bank fees
Add new> Name - Bank fees > checkmark I sell this product/service to my customers.> Income account - dropdown menu select Bank charges > Save and Close.
Now include this item with the negative amount of -50 and Save the invoice.
This will increase the bank charges and reduce the amount owed by the customer.
Comment back for further clarifications / to discuss.