Try temporarily disabled two factor authentication to see if that is the cause.
If not, the problem could be with Internet Explorer on the computer, make sure you are able to login using IE on the computer as that is what the popup window in vMix uses.

Just setup a test with Login Approval enabled and it worked ok here.
After logging in, it asked to send the login code to my mobile, then on the next screen it prompted to type it in.
After doing that it goes through the usual app approval process then the logged in account shows up in the vMix Facebook Settings screen
as logged in.

Do any of these steps differ to what you see when logging in?

I'm using the latest 18.0.0.59 for reference.

Regards,

Martin
vMix

I solved the problem of connecting vmix to the facebook account as follows: I installed a lower version of the present one, that is vmix 22. I installed vmix 21. There vmix linked to the facebook account without any problems. Then I updated the program to version 22. He asked me again to log in and, to my surprise, it went away. At the security requirements, we asked for the code (the confirmation was done on the mobile phone, where I installed facebook). It seems that, installed from the beginning, version 22 has a problem with the association with the browser when it takes the login data from the facebook account. So this is the solution. That's how it went with me.