When attempting to login to the WHM or cPanel interfaces, the error "The login is invalid" is reported at the top of the page.
This error means that the credentials provided by your authentication attempt were rejected. This is commonly caused by either inputting an invalid password or if the authentication attempt is blocked by cPhulkd.
To ensure the credentials are correct, you can try logging in through SSH as the user. This will not be prevented by cPhulkd, so authentication failures would indicate the incorrect password is being used. You will need to reset the password for the affected user to ensure the correct one is in use. Please note that cPanel support is unable to assist with password changes.
If the correct password is being used and you can access SSH, can use the cPhulkd command-line tools to whitelist the IP you are connecting from to prevent further blocks. The following command can be used by replacing the example($IP) with your actual IP address.