If I owe more after I amended but have to mail in my new forms. Do I pay the IRS online now? Or do I mail in my papers, wait for them to be accepted, and then pay?

I finished my return using Turbo Tax online.
My return got accepted.
I forgot a 1099-NEC in my drawer.
Amended my return, owed more money.
Amended online through Turbo Tax.
At the end it said print out these papers, send to the IRS with a check.
Instructions said I could pay online.

The amendment checklist says I can pay online, but the file by mail instructions say “ your federal amended tax return shows you owe a balance due of ____. You are paying by check.”

So which is it? I would love to pay online instead but should I just go the money order route? (No checks). Should I pay now online? Should I send files first and then pay online?

Would like some clarity, thanks.