I play EA FC 24 on switch, how can I log into the Companion app?

I play EA FC on switch.

As far as I can remember my EA FC Account was created automatically by entering with my switch account.

Therefore I assume that my EA FC account is directly linked to my Nintendo account. Can somebody confirm that please?

So I never created the account and/ or defined a password specifically for EA FC.

My question:

Which credentials do I have to use to login into the Companion app?

// I used the email and password of my Nintendo account, but Companion does not accept these.

Important: This EA account from which I am posting here is not the one linked to EA FC. Although both accounts this EA account and my Nintendo account share the same email address.