How do I verify trust of third-party apps on my iPad mini 5th gen?

When trying to open the app, it tells me that it’s impossible to verify the app. Here is a print.

This is when I try to open Scarlet. I have already gone to Settings>General>VPN & Device Management>Sunshine Insurance Group Co., Ltd.>Trust this app.

Also, I already tried it with other devices and with different internet connections but I just can’t… Do I need to do anything more?

Thanks for reading.

[Re-Titled by Moderator]