If you have online banking you can do the payment yourself, just ask the bank for their account name, sort code and account number.
Personally I wouldn’t be happy using a 3rd party financing company (which is what Bumper is) to have any part of a transaction between myself and the garage. The less people involved the better, and I certainly wouldn’t let them have access to my face or fingerprint.
Please excuse spelling/typos. Apart from being a clot it turns out I had one on my cerebellum that's now causing various problems!