Issue with adding Voip phone to Zoom

Hi, I signed up for the Zoom phone metered plan ($12/ monthly) and after trying to add my Poly E350 Voip phone by using the MAC, I continue to get an error message stating “Extension 800 requires a Zoom Phone Metered, Unlimited, or Pro plan.” Please see attachment  

Is there something I’m missing, or do I need to upgrade the plan again in order for me to add the phone? Any advice is really appreciated. Thank you