Turn on a multi-functional pressure cooker (such as Instant Pot) and select Sauté function. Add oil and red curry paste to the hot pot; sauté for 30 seconds. Add chicken and mix well with curry paste. Pour in coconut milk. Close and lock the lid. Select high pressure according to manufacturer’s instructions; set timer for 2 minutes. Allow 10 to 15 minutes for pressure to build.

Release pressure using the natural-release method according to manufacturer’s instructions, 10 to 40 minutes.

Unlock and remove the lid. Stir in fish sauce and palm sugar. Stir in onion and bell peppers until well combined. Select Saute function. Bring curry to a gentle boil and simmer for only 2 to 3 minutes to keep vegetables crunchy.