Probably you never logged in to any OpenAIRE service or the email associated with your account is different from the email used for inviting you to become manager or member of the gateway.
Go to OpenAIRE EXPLORE and check the user information you can find by hovering on the initials on the top right. Inform the manager and ask them to invite you using the email address you see in the user information page. (mini video tutorial from 00:30 to 1:00)