Can not add line items to payment_reference_field

This is very probably related to older issue #2840698: Ajax broken in payment_form submodule but that issue pertains to payment_form_field. But something similar occurs on payment_reference_field (PRF). Problem occurs locally on a fresh install and also on simplytest.me.

Steps to reproduce:
- Install PRF submodule
- add a PRF to content type
- when doing config for the field, click "Add and configure a new line item"

Problem noted:
Nothing happens.
(instead of the expected subform for a line item appearing) see Selection_075.png

I also noticed that if you:
- be stubborn and click the button a few more times
- give up and click the 'save settings' button anyway
- the fields DO show up (and also the validation errors for those fields) see Selection_076.png
- fill in the line items' fields and 'save settings' again
- edit the field settings and they get saved (and validation checks are passed)

Marking as major for User interface.