What is the best alternative for tomatoes in chicken curry?

Tomatoes can be a fairly fundamental part of a curry, and attempting to substitute them would change the dish radically. I suggest instead you look for a recipe that doesn't use them in the first place (sauces based on things like yoghurt, slow-cooked onions, or coconut). You could use a similar mix of spices to your favourite tomato based recipe, but it would still be very different overall.

You may find that people like well-cooked and blended/chopped/sieved tomatoes even if they wouldn't like fresh tomatoes cut up and added towards the end of cooking (I'm not keen on nearly raw tomato myself). In this case using tinned tomatoes instead of fresh could be sufficient.

I have tried adding other acidic ingredients, such as lemon, to compensate for what tomato adds to a curry. It doesn't work with dairy, but it does work with nut-based milks (coconut and cashew are my go-to for curry). It won't substitute anything by itself, but it still helps balance out the flavour profile that's thrown outta wack from lack of tomato.

I have anecdotally observed warm spices we associate with tomatoes can set our expectations to imagine tomatoes where there are none. Try increasing the spices and vegetables in the curry that are common to other tomato sauces as well! Red chili is a safe bet if you're already using lemons to add acidity.

You want to find things that fill in the blanks of missing ingredients, on a case-by-case basis, when you dedicate yourself to substitution. Most creative people are aware of this, but what separates reasonable logic from creative genius is your ability to triangulate with related recipes to find variables you can plug different stuff into. In the same manner, this process can be as intuitive or technical as you want! It's all about consistent practice, experimentation, and proper feedback. That's what I keep telling myself during the process of food magic ;)

Tomato paste, according to menu, ie 2/3tbl spoons per 500grm meat. Can add a squirt of tomato sauce for that hint of sweet at end before serving.