I can’t access the money in Apple Wallet because my side button doesn’t work

Just to set the proper expectations, your side button is a mechanical button and it could fail for various reasons.

Is your iPhone less than a year old and under the standard one year manufacturer’s warranty or if older do you have Apple Care?

It’s possible to change settings on your iPhone to enable Face ID for transactions, but, unfortunately, is fairly extensive.

Please let us know how to best assist you.