Add chili sauce, grape jelly, water, red pepper flakes, and garlic powder to Instant Pot. Stir to mix.
Add meatballs and stir to coat them in the liquid.
Place lid on Instant Pot. Make sure valve is in "sealing" position. Set to Pressure Cook for 8 minutes.
Release pressure manually and carefully remove lid.
If you want the sauce to be thicker, mix the cornstarch with 1 1/2 teaspoons of cold water. Add to the pot and stir it into the sauce. Set to "Saute" mode and let simmer for a minute or 2 to thicken.
Sprinkle with green onions before serving.
Notes
Note: Cooking time does not include the time it takes for the Instant Pot to pressurize which will be about 10 minutes.Be sure to use a chili sauce that is similar to ketchup, like Heinz Chili Sauce, and not an Asian chili sauce.