Pour coconut milk, chicken stock, Thai red curry paste, fish sauce, soy sauce, brown sugar, garlic, ginger, and red chili flakes into the inner pot and whisk until well combined.
Add the chicken breast and vegetables making sure the chicken is fully covered. If needed add more chicken stock.
Select SLOW COOK-Custom-High and set the time for 9 hours, press START.
Close the Pressure Cooking Lid on the Instant Pot and set to pressure release to VENT.
When the time is done, remove the chicken breast and cut it in chunks and stir back into the inner pot. Adjust the seasoning with salt and pepper.