Mix all the dry rub ingredients together then rub the mixture in the cavity of the chicken and all over the exterior of the chicken.
Place the onions in the cavity of the chicken.
Remove the lid from the Instant Pot and remove the rack. Next, pour the water into the stainless steel liner.
Place the chicken on the rack. Lower the rack into the Instant Pot stainless steel liner using the handles of the rack.
Properly seal the Instant Pot and set the vent to "sealing".
Set the Instant Pot to "high" pressure and set the timer for 34 minutes. (Or 8 minutes per pound of chicken.)
Once the chicken is finished cooking, allow the Instant Pot to come down from pressure naturally, or release the pressure moving the vent from "sealing" to "venting". BE CAREFUL! If you release the pressure in this way, steam will surge out of the vent. I prefer to allow the pressure to come down naturally.
Once the pressure has been released, open the Instant Pot, and remove the lid. Lift the chicken out of the stainless steel liner using the handles of the rack. Transfer the chicken to a serving plate and enjoy!