im trying to download the my tmobile app and itunes want let me

You need to have valid and verified payment method for your account.

It for some reason your payment method was unable to be charged you won't be able to download anything, even free apps or updates until you can verify it again.

Follow the steps here to review your payment method, and get it verified.

Change or remove your Apple ID payment information - Apple Support

Follow the steps in the link above to change it to a payment method that can be verified. Once its verified correctly it can be removed, and set to "None" and won't need to be verified again.

Steps to get it changed are here:

https://support.apple.com/en-us/HT201266

Hi,

Make sure your iPhone's operating system (iOS) is up to date prior to downloading apps. It should be running v10.3.2.

Tap Settings > General > Software Update