Yes, the convenience fee is only charged to credit cards and not bank transfers or checks. This is a fee charged by a seller when a consumer pays with an electronic payment card rather than by a standard form of payment accepted by the business.
On the other hand, to change the % rate of the convenience fee on invoices, you'll need to edit the service item you used on the entry. To do this, I'd suggest going to the Product and Services page.
Click the Gear icon in the upper right corner.
Choose Product and Services.
Locate the Service item for convenience fee that apply on invoices.
Click the Edit link under the Action column.
Go to the Sales price/rate box and change the amount% rate.
Hit Save and close.
Once done, you can go to the Sales page and locate the invoices. From there, you'll need to change the % rate of the convenience fee of the entry. To do this, please make sure you toggle the option to another item and select again the convenience fee to save the changes. Please follow the steps below.
Click the Sales menu at the left panel.
Choose All Sales section.
Locate the Invoices and click it to expand the page.
Change the service item to another one. Then, select again the Convenience fee.