Arcadier marketplaces allow you to sign in to your Admin Portal using either your email or username and password, or by using your Google account.
To access your Admin Portal, open a web browser and go to https://yourmarketplacename.arcadier.io/admin. Make sure to replace yourmarketplacename with the actual name of your marketplace. This link will still work even if you are using a custom domain.
Do note that you should be logging into your admin portal on web, and not mobile, as it has been optimised for web only.