Usage patterns
〈人〉に使者を送るto send an envoy/messenger to someone
The king sent an envoy to the neighboring king.
使者として〈場所〉に行くto go somewhere as an envoy/representative
He went to Kyoto as an envoy.
〈人〉の使者someone's envoy/messenger (acting on their behalf)
He came as the president's envoy.