Do you mean IVPN ? If it is, unfortunately there is not flatpak equivalent for it. You can ask them to support flatpak or make a package request for Solus repository.
The only other alternative is to just not use their app and just use their guide on how to set it up via NetworkManager (WireGuard/OpenVPN). I use this method to setup ProtonVPN, I prefer it this way.
Solus will support snap (at least) until end of the year. No need to rush migrating your app.
