K and N checkmate????

It is possible to checkmate with only a knight or a bishop, if the opponent has more than a king on the board.

from google. Checkmate with K+N v K is not possible. The game ends in a draw by insufficient material.

It isn't possible to mate with only a knight or only a bishop. K+B v K is also an automatic draw.

The position here above is clearly won by black since a mating position exists (after pawn promotion to bishop)

Mate is possible if opponent cooperate with helpmate. Otherwise draw.

Then why did it give my opponent the win.

Lichess faq says it is possible........I would like to see how k and n mate if so

@svfox Note that what you found on Google specifically says KN vs K - in other words, one side has only a king and knight, and the other side has only a king. That is impossible. It does not say it is impossible to ever mate with only a king and a knight.