The first and quickest thing to try is to reload the page in your browser, to see if that sorts our the issue.
Close all tabs in your browser and then close the browser app, before then opening the browser again. You can use the "Save and Finish Later" tool to get you back into the check quickly.
There may be apps running on your device which are using the camera in the background, which may be interfering with the process.
On iPhone and iPad, the Chrome browser does not support the same fatures as the Safari browser, so if Chrome is not working then try Safari instead.
You can also try restarting your phone/tablet entirely.