This one is a head scratcher. I cannot figure it out…

I’m developing a formula column where our payables person will see a message like this: “On xx/xx date, pay $350.00”. I get stuck trying to get the dollar amount on the formula because the amount comes from different columns, depending which payment number the project manager is trying to make .
On the board, each payment amount approved by the PM is recorded on its own payment column (e.g. pay #1 column, pay #2 column, pay #3 column, etc.). So, if this week the PM approves pay #2 for Joe Painting Company for $350, how do I put in the formula to insert Pay #2 amount, not Pay #1 or others? At this point, Pay #1 column has already been filled out, and the other payment columns (not #2) are either empty or “0”

you pay the amount on the column that is next (left of) the column that is still “zero”. For example, Pay #1 column : $300, Pay #2 column: 350, Pay #3 column: 0
Then we know we have to pay the amount that is in Pay #2