A User ID identifies the specific user of an account.
If your account has more than one user, you log in by filling in your USERID, your payment service provider ID (PSPID) and your password. Please make sure you click on the 'Log in as user' link so that all three fields are displayed.
If your account only has one user, you will not need a USERID. You will log in using only your PSPID and password, so please make sure your login screen only displays two fields. If you can see three fields, click on the 'Log in as PSPID' link on the bottom left of the screen to log in as a merchant.