Enter the confirmation code

Hello, I wanted to add a passkey to my Firefox account, and to do so, I need to receive a confirmation code sent to my email address. However, this code is not arriving. My email is an alias (email forwarding is enabled). I have tried requesting the code multiple times, but unfortunately, I still cannot receive it. Furthermore, when I try to add an alternative email address - so that the verification code could be sent to a different mail - I am also required to authenticate using my primary email. How can I resolve this issue? Thank you in advance!