How do I install an app not available in my country or region on iPhone 15?

I have an iPhone 15 that I purchased while living in the US. I now live in Panama and I cannot download and install the app for my Panamanian internet provider.

I have changed my region, logged out of my Apple account, restarted the phone, signed back into my Apple account and I still receive the message that the app is not available in my country or region.

Is there someone in this community who can help me fix this???

Thank you,

Elisheva

[Re-Titled by Moderator]