Because Reddit shut down third-party access for apps that don't pay high fees, Sync will show a "401 error" or fail to load content unless you "spoof" it using your own developer credentials.
: You must visit the Reddit Apps Preferences page to create an "installed app." The generated Client ID (a short string of characters) must be entered into the ReVanced patcher during the setup process. Sync for reddit (Pro) Mod APK v23.02.02-21_38 (Pro).apk
“Protip for Sync users, in Options under general settings you can turn the update notifications off.” Reddit · r/Android · 2 years ago Because Reddit shut down third-party access for apps
“Only took 45min max... just install the last version of sync from apkmirror, then follow the prompts in revanced manager it's really simple.” Reddit · r/revancedapp · 2 years ago Sync for reddit (Pro) Mod APK v23.02.02-21_38 (Pro).apk