Inability to sign to iPad app post password change

[MusicalSociety]

Hi all

We use Square for box office and bar sales for our community theatre.

We have 2 ipad Gen 4's that are only up to IOS 9 and as far as we can tell are only supported to IOS 10 based on a quick google search.

Just before we were to use them the other night we were prompted to change our password which we dutifully did. 

Unfortunately are a result of this the app on our iPad's will not accept our logins anymore and as such we are unable to use them as we cant get into the program to pair devices and carry out transactions etc

Luckily I had my personal iPad handy to use as a substitute which I think is updated to IOS 15 or close to that. 

My hypothesis as to why these are not working is because the new app I tried to download (it was the only way I could think of to try and work around the problem)  says it is only for IOS 13 or greater and as such the current app on these old refurbished iPads of ours will not work.

Can anyone tell me if this is correct or are we doing something wrong to get this ipads up and running again??

We don't want to have to pay for new  ipad or new tablet/square device unless we have to, as being a community group money is tight.

These ipad 4's are purely for Square use so have no other applications used or running that I am aware of. 

Any help you can offer greatly accepted