Hi and welcome to Digi Forum.
most recent HW models have a unique password printed on the label, so I would suggest to check and if you have, please try with that.
Also, depending on the firmware loaded into your WR21, the default username may be "admin" instead of username.
Then, if still issues, please try in an incognito mode and/or erasing the cache of the browser.
For any further help, please review our support options on our website: https://www.digi.com/support
Digi Technical Support Team