My iPhone 6s didn't turn on I plugged it and it was showing charging then after thirty minutes it's not charging and it didn't power on

See this support guide:

If your iPhone, iPad, or iPod touch won't charge - Apple Support

If you get no help, it could be a battery problem. I would make an appointmente at your most convenient Apple Store or Authorized service provider and have your iPhone inpected. They will diagnose the issue and give you all the available options:

Apple - Find Locations - Location Selector

Regards

Giulio

I'm having the same issue with my iphone 7. After a while it did start charging but again stops. It's very intermittent.

Please, read my previous answer to the Original Poster.

Thanks and regards

Giulio