I have a problem logging in, I can’t create a new account how can I fix it? and I can’t register with FB
New accounts can no longer be created on Legacy, it is being discontinued.
If you have an existing accounts which has been used recently, then doing password recovery (and checking your junk mail folder) should allow you to log back in.
If you haven’t used your Legacy account recently then it may have been deleted to comply with GDPR requirements and to save server space.
FaceBook login was removed by Facebook quite a while ago.
Either way, I suggest that you migrate to Blynk IoT before Legacy is turned off.