I finally found a solution! 
After logging out, I went to Cursor > Editor Settings and disabled the Http2 setting. Then, I logged in again, and everything started working properly.
I hope this solution helps more people facing the same issue.
Endless praise to “fei.hu” from the link below—you are the savior of my day! 
Cursor tab does not work and Requires pro (custom model) - #9 by deanrie
