magentatechie is correct -- there's likely a block on your account. Do you have a prepaid or postpaid account? If prepaid, short code services may not be available. If postpaid, this is likely happening due to a content block and working with T-Force over Facebook or Twitter is recommended to get the block removed.
Quickest way to resolve this was through Facebook Messenger! After spending 2 hrs on hold waiting to speak to an agent, I got no where. The agent kept insisting that I need to add money to my account and I insisted that unlimited texts means unlimited!! And I was receiving some short codes just not the one i needed to complete the Zelle transfer. My bank was sending the codes yet t-mobile was blocking it. After messaging through FB, they enabled ALL short codes and my Zelle was completed in no time! Do not pay extra for something that is already included in your plan!! Good luck to others with this issue!!!