Xbox asking my friend for a payment plan to access multiplayer

Game Pass Core or Game Pass Ultimate (which includes Core) is required to play online in most games. If you've never had a subscription yourself, it's likely someone else has used your console and set it as their Home console so you would be able to play online using their subscription.

Just to be clear, you are on the payment plan and didn’t just buy one right? Game Pass only comes with the All Access payment plan

That sounds like a great plan, I would suggest doing that as if its not asking you for secondary payment 3 months ago, looks like prepaid is not asking for secondary payment method.

Unfortunately if it asks for a payment method, you need a payment method. The cards start a recurring subscription so you have to have a payment method on file for future payments, even if you plan on turning off recurring billing.

Only if you bought it though the All Access 24 month payment plan. The standalone does not come with subscription.