Dear @hsinnyliu,

Please make sure you've correctly filled the URL field, as shown in the screenshot below.

Then navigate to Dashboard > Forums > Settings > General admin page, jsut click on "Update Options" button. 

Then one more time delete all caches and check again if it doesn't help Uninstall (not deactivate) and install wpForo again. The uninstall will remove all forum data and rest it on a new installation.

Hi Sofy,

My problem is solved.
Thank you very much for replying to my question every time.