Hey there Bri2005_18,
Since noticing this error, have you made any changes to your country in the Settings app on your iPhone? If so, this could be causing the error to appear.
Also, make sure you have the latest software installed to ensure everything is up-to-date and compatible. To update, go to Settings > General > Software Update.
If the issue persists, please connect with the app developer directly:
Open the App Store on your iPhone, iPad, or iPod touch.
Search for the app, then tap it. If you can't find it, tap the account button or your photo at the top of the screen, tap Purchased, tap "Not on this [device]," then tap the app.
The app's product page appears. Scroll to the Ratings & Reviews section, then tap App Support. If you don't see App Support, make sure that you're signed in with the correct Apple ID.
You'll find those steps here: How to contact an app developer - Apple Support
Take care!