account trouble with Horizon Link App

I have a Meta account for years, and also have/had an Occulus account since 2017 as I wanted to buy a PCVR title for later. I have many Quest tittles and also PCVR (Rift store, many cross-buy) titles which I never used, because I had no PC. Now I bought a PC and try to use the Horizon Link App. After installing it wants me to enter my Oculus account data (which I find strange, because I thought it's all meta now). I did so (with my old Oculus account) and it says they are wrong. Then I tried my Meta account data (with the same email address), although it says “Oculus” and not “Meta” (for whatever reason). That also did not work. So I gave my Meta account a fresh new password and tried to use it in the Horizon Link App. It still says they are wrong.

Please help. It would be sad if I would not be able to use all those titles I once bought for later use (Lone Echo, Stormland, etc) and also the cross-buy titles.