Customer added with Invoicing plugin from https://wpgetpaid.com/ cannot be selected

Hey our plugin adds User level Customers just like the WooCommerce and that is the user level which works everywhere in our plugin. 

You cannot select any other type of user. You can send me your logins i will see if something is possible thanks. 

Hello, thank you.

I am going to try looking at a few things regarding User Level Customers and I will get back to you if I can't solve the problem.