I'm wondering how to add a new custom payment acquirers for payment types that are not connected to any external service?

I'm trying to add "Payment on pickup on location" and when I select it on the website on order confirmation the button just gets the spinning icon and nothing happens. 

I've left the default_acquirer_button in Form button. For provider I've selected Manual Confirmation.

The only documentation that I've found for setting Payment Acquirers was for odoo 13 and it said that I should configure the template like it's in the documentation of that payment service. But I don't need a service, it should only show the confirmation page.

So can anyone help me how to create simple Payment Acquirers?