I iPhone 6s Plus is not taking charge.

Hi

Follow the steps here:

https://support.apple.com/en-gb/HT201569

If you battery health is showing less than 80% then more than likely you need the battery to be replaced.

when that happens to me I use a toothpick or match to clear out the dirt and the lint in the connector that always fixed it

of cause you may wish to try other cables and chargers to rule them out as the culprit

and of cause the connector itself could also be damaged

What is the battery health?