Adding payment details

I work in a school and need to download an app to several ipads. I use Apple School Manager but the app does not allow me to install under a different id to the one on the ipad as it will not then run.

Therefore I have to use the same banking details on each ipad then remove them after I have purchased and installed the apps.

I have been successful with several ipads now I have a problem and it says I need to contact iTunes support co comlete this transaction. It will not go further than entering the details and when I click done it goes back to the add payment page with the red alert as stated.

Please help I need to do these before mid next week?

Thank You Seal