In order to sign into a Modrinth account, always ensure you use the same provider or linked email address used during initial registration to access your account. You must select the same method you used to create your account. For example, if you used Google to create the account, you must use Google to log back in, unless you change the authentication methods from your Account Settings.
If your account was created on or before August 5th, 2023, your account was created using GitHub. Attempting to reset your password or log in through any other service will not work.
If you are encountering a "400 Bad Request" error when signing in saying "User email/account is already registered on Modrinth", you already have an account using one of the available sign-in options. You must use the same method to log in as you used to initially sign up. Verify the provider or email address linked to your account by checking email notifications, as mismatched information can cause login errors.
If you still cannot log into your account, please file a request with support. Before doing so, ensure you have tried all recommended troubleshooting steps, such as verifying your credentials and updating the app to its latest version.