Do you have ‘LTE’ enabled on your phone? This is a necessity to enable connection to the VoLTE(4G) network. 4G is only a label for the 4th Generation network and not the the ‘actual’ type of connection which is VoLTE (Voice over LTE). It is worth doing an internet search to see if you can find an answer e.g. how to enable VoLTE on (make/model)
Do you have ‘LTE’ enabled on your phone? This is a necessity to enable connection to the VoLTE(4G) network. 4G is only a label for the 4th Generation network and not the the ‘actual’ type of connection which is VoLTE (Voice over LTE). It is worth doing an internet search to see if you can find an answer e.g. how to enable VoLTE on (make/model)