Keep getting asked for username and psw

Hi,

I am having issues with WP at the moment. I installed a new theme (FireUP) and whenever I click on Appearance —> customise I get asked for username/psw. I enter them, a message pops up telling me that they are correct and then ask me for username/psw again, and so on and so forth.

Could you please advise what the issue is?

Thank you.