Looking for logging into the Sandbox site and are not getting the correct working link for it? In such a case, you can use the links given here by searching your desired login page in the search box. If the page is present on our website then you will get all the links related to the Sandbox site. After that you can login as usual with your login credentials.
https://developer.paypal.com/developer/accounts/
https://developer.paypal.com/docs/classic/lifecycle/sb_about-accounts/
https://sandbox.braintreegateway.com/login
https://sandbox.2checkout.com/sandbox
https://stackoverflow.com/questions/15337235/how-to-log-in-in-sandbox-paypal-account
https://www.runsandbox.com/
https://login.salesforce.com/
https://developer.salesforce.com/forums/?id=906F00000008kVjIAI
https://www.braintreepayments.com/sandbox
https://system.sandbox.netsuite.com/pages/customerlogin.jsp
https://accounts-sandbox.dwolla.com/
https://www.paypal-community.com/t5/Sandbox-Environment/Can-t-Login-with-Sandbox-Acct/td-p/1503624
https://salesforce.stackexchange.com/questions/215697/what-is-my-username-and-password-when-i-clone-a-sandbox