If the Interface is not recognizing your credentials as valid, you will be facing this message:

The most common cause is actually a typo or wrong credentials being used (frequently, due to extra whitespaces added at the end). 

Check for capitalization, spaces, misspelling issues. If this is not causing the problem, clear cache and cookies and try again.

It is also advisable to check for auto-fill options in the browser that may be inputting the wrong data automatically.

If the issue persists, reach out to customer.happiness@unbabel.com or use or support form mentioning the exact username being affected.