Adding Gmail account to flatpak-based BlueMail app on Silverblue 37

Hi. I just found BlueMail in flathub (I already used this app on Android for quite some time). I am unable to add my Gmail account to it (my university Microsoft account went just fine). When I try the automatic option, it open my browser, I grant the required permissions and click continue. Then, nothing else happens. The app stays in the waiting phase. I suspected a permission issue but in flatseal I am not sure what to try. I tried a manual configuration but it failed too. No progress with the rpm version, so I stick with flatpak. I found several other issues with the app but this one is the only critical. I even checked my Google settings and BlueMail shows (at least for the Android flavor). Any ideas?

BlueMail is proprietary, closed-source software by Blix Inc. Please contact their support for program-specific bugs and settings.

Thanks. Yes, I know BlueMail is propietary and I intend to contact support. But so is Mailspring and other email apps I have tried on Linux and never found an issue like this. Since I am running Silverblue, I though there was a better chance to find assistance in the forum.