Use a known-working, MFi-certified Apple cable and wall adapter. Cheap, non-certified cables often damage the internal charging IC.
Use a toothpick or compressed air to remove lint from the charging port. iphone-6-no-power-solution-100-working
Plug it in for at least 30–60 minutes before attempting another force restart. Use a known-working, MFi-certified Apple cable and wall
If the battery is completely drained, the phone may not respond immediately. Use a known-working
Often, the phone is powered on but "frozen" with a black screen. A force restart can jumpstart the system.
Keep holding both for at least 10–15 seconds until the Apple logo appears. 2. Check Charging Components