I am logged into production. Trying to install (Box) from AppExchange into a sandbox. I can't get logged into the sandbox, though. It prepopulated Username, but my password isn't working.
I've tried a dozen different permutations of credentials following the advice of several threads here (notably, How to login into a sandbox from Sandboxes page in Production org?).
I've been trying to log in for a full hour and I'm no closer...