I called UA and she said "yes", but she could not take payment over the phone, I had to do it on-line.

I've tried several times....it's the balance left from some Covid refunds, we have used up most on other flights (including the one in a few days), and have $19 left which I wanted to put towards one checked bag.

I go through the whole thing of putting in the 10 digit pin, name, and then there is a box that says "ADD" - Add what? the box doesn't do anything, I keep getting the message "find your travel certificate number", which I already have.

Keeps going round and round in circles.

Can anyone help?