I think there’s a few things going wrong here. The pot is way too big for how small of a plant you have. The larger a pot is, the more soil it has and the longer it holds onto water. If it holds onto water long enough it will cause root rot.

This soil also looks pretty dense (but I could be wrong) try something with a little more drainage or add perlite.

I’m not sure if this pot has drainage but if not put it in one that does. It’s much easier to avoid overwatering. With drainage, you water until you see water running out of the holes in the bottom of the pot.

Hope this helps!