You have the option to manually record the Square fees by editing the invoice, and add another line item for the fees, and enter fees in negative amount. Or, create a deposit transaction to record the square fees. First, check or create an expense account for the Square fee. Here's how:
Click on the Accounting tab.
Click on Chart of Accounts, (search merchant fee or square fee), if none shows create a new account.
Click on New.
Set Account type as Expense.
Enter Name like Merchant fee or Square fees.
Click on Save.
Next, is to create a Service/Non-Inventory item in your products and services list, make sure the income account field is set to the expense account created above. Here's how;
Click on the Settings icon.
Click on Products and Services.
Click on New.
Select Service or Non-inventory type.
Enter Name as Merchant fee or Square fees.
Under Income account, select the expense category created earlier.
Click on Save and done.
Then, create a deposit and record the fees in negative amount. Here's how;
Click +New button.
Click on Bank Deposits.
Select the payment.
In the Add funds to this deposit field, choose an account.
Enter a negative amount, under Amount.
Click Save and close.
Once done, if there is a downloaded payment in the For Review tab you can Match the transaction for that invoice.