"callto:<email>" links can't finduser but "sip:<email>" can

As in title: why is this happening. I'm developing a contact manager for a company and everything works like a charm except this. I know I've managed to make it work once but since then I always get the same error on the callto protocol: Can't make the call, user not found. I have this person in my contacts and can call them normally from within teams contacts.

What I can't wrap my head around is that sip protocol correctly opens' the user's chat window, although they don't seem to receive messages I send, but I can call them, which is what I was going for.

Does anyone know what might be going on?

Edit: on further testing, I noticed even SIP actually finds their Skype account, not Teams account. Now what's going on there?