If customers receive an “Invalid username or password” notification while logging in to your online store, this may have two causes:
Incorrectly entered login details
Check whether all data has been entered correctly. Note: The password is case-sensitive!
Payment made as a guest
The other possibility is that they most likely placed an order as a guest. In that case a customer file is created in the back office (because an order must be linked to a customer), but not a customer account. For this, customers will first have to register. This can be done as follows: If they click “Forgot password?”, they will receive an e-mail containing a password reset link, enabling them to configure a new password, and, in this case, create one, which they subsequently can use to login. The guest account will be automatically converted to a customer account.