Outgoing iPad mobile calls (via iPhone) are not available (Contacts app)

I have the exact same problem as u/ronfel here: https://discussions.apple.com/thread/251353164

When I receive a call to my mobile phone, I can answer it from my iPad. But I can never initiate a phone call from the iPad itself. I can switch a call from the iPhone to the iPad when I start it from the iPhone, though.

It says "Your iPhone must be signed in with the same Apple ID for FaceTime and iCloud to make calls from this iPad". I can assure you that I'm logged in within the same Apple ID on both devices, I have all of the options in Settings enabled (in Phone and Facetime, on both devices) and I have tried turning them on and off.

Now, I suspect this might be an iOS bug itself, if I'm not mistaken this was on iOS 13 too. Please either elevate this higher or propose a solution that wasn't mentioned in the u/ronfel's thread.