Solution to Zwift won't connect to Garmin Account

I’ve been have this problem for a while, and tested all solutions and none work. Now I find maybe the real solution:

Go to Garmin Connect the APP on your phone
then goto
Setting-Connected Apps

then you should find you have already have Zwift connected, and might be multiple, in my case, I have 4 or 5 Zwift already connected.

Deleted them all.

Then try to reconnect Garmin account on Companion, it should connect now.

This is so tricky not to connect Garmin thing, I’ve been doing manual upload for at least half a year, I can find someone to discuss it, but not everyone discusses it. So I tried to find if the bug is on Garmin’s side. It’s kind of Garmin creates slots for 3rd party connection, and might be we delete Garmin from companion, it didn’t clean these slots. When these slots are full, no more connections can be added.

Now, Bingo.