I’m using EE4, and I know that you can normally remove Invoice as a payment option in the setting page; however, this is not an available option any longer. I have installed a few EE premium plugins and we are using PayPal express buttons for payment. The Invoice option has completely disappeared.
It’s normally available on the Event Espresso > Payments page. If it’s not there, then what you can do is head over to the Event Espresso > Maintenance > Reset page, then you click on the “Reset Event Espresso Capabilities” button. This will restore any missing capabilities that may have been accidentally removed.