The phrase "successful login" means that someone was able to enter a computer system or website by providing the correct username and password. Full definition
If the encrypted login code is correctly verified, the game server may then log in to the user's gaming account and send a notification of successful login. (patentlymobile.com)
If you have a checking account / saving account / CD or a credit card account, you will see link in the special offers section, «Add It Up» on account summary page (the one you get immediately after successful login). (financeproductreviews.com)
The iPhone X occasionally pulls images from successful login photos to update its database. (dealntech.com)