I don't know what you have tried, but we are having some success with the following:
No added sugar ready brek run through a sieve and served with apple puree (ready brek is fortified with vitamins) and we all have it for breakfast, in the morning, which is when my LO is most relaxed and happy. (The sieve isn't necessary, but my LO finds lumps offputting at the moment).
Serving a mix of purees and solids on the same plate (my LO gets some puree on her fingers and sucks it).
Making purees as smooth as possible to start, if you struggle with this try Ella's kitchen first foods. My LO particularly likes the pureed carrot (she isn't as enthused when I make it
).
Lots of praise, make it fun. Don't put pressure on, keep it light and happy, very smiley and 'oooh, isn't this yummy?'
Try a small amount of lots of different foods, I aim for a baby-sized handful of each and between three and five different types. Make note of what baby seemed to like and serve again next time. Revisit disliked foods a few days/weeks down the line - tastes change!
I haven't tried this myself yet, but when they're very good at sitting up unaided, as I imagine yours is, someone on here once suggested putting them on a clean shower curtain on the floor and just giving them finger foods as toys to make it fun.
Good luck!