When attempting to enter varying amounts on youth accounts, I clicked on “Enable Custom Amounts and Notes” and proceeded to check the youth names and enter the varied amounts. When I clicked on Update I got an error that says “Amount: Please enter a valid Amount” with the Amount field at the bottom of the page highlighted.
The developers have been notified and a fix will be released shortly. In the mean time, you can enter any amount in that field, and since you have custom amounts entered it will not affect anything.