Why? Sololearn write me:

Sololearn write me: username not found freecodecamp. Why?

For any problems with connecting freeCodeCamp to sololearn, please contact sololearn. There is nothing we can do for you.

Please see this thread that has an explination from our founder Quincy Larson:

Here is the sololearn support you can use:

Please see what they said:

IMPORTANT NOTE
the account linking is implemented at SoloLearn side only!
please refrain from asking about it on their forums!