After user clicks the login button and approved permission he redirect to this:
https://...domain.../mytiktokapp/callback.php/?code=XXXXX&scopes=user.info.basic%2Cvideo.list&state=YYYYY
That lead to page 404 because the slash after callback.php
In the manage app setting the redirect URL to this:
https://...domain.../mytiktokapp/callback.php/
I can't remove the slash / in the end - Added automatically after send my app to Tiktok review. https://prnt.sc/MWbBBMpNqZAL
In address bar in the browser if remove the slash and click enter all done well. The user info download according to my request for scopes user.info.basic, video.list
Trying contact Tiktok to remove the slash in the app setup redirect URI, but waiting them to answer.