Request you to perform some troubleshooting steps shared below to resolve the issue:
Ensure that you are using Samsung original charger for charging the device which is provided in the box.
To increase the charging speed, turn the device or its screen off when you charge the battery.
If the fast charging feature is not activated, launch the Settings app, tap Device care →Battery → Settings, and then tap the Fast cable charging switch to activate it.
If issue still persists, register your concern in Samsung members app (Open Samsung members app>click on”+” icon>send feedback> Error report/Ask question)
