Issues with integrated flash

[Sirob]

Hi

I'm new in this community and new in photography, especially with Fuji. I just bought a X-S10 which has been great until I tried the integrated flash.
With my flash on TTL mode, low light environment and the lightning symbol popping up every time, the flash doesn't always fire. It fires only randomly and even when it does, the exposition of my picture is wrong. The pictures are always too dark or too bright... I made a video to try show the problem better. I hope it's understandable. (see below).

I seeked help from friends and people I know, but no one was really able to tell me if it's a problem of settings or a problem of my camera. I'm thinking about returning it under guarantee, but first I wanted to see if someone here could maybe help me.

Best,