participant "Patient Registry" as PR

control "Match-Connect" as MC

control "Search & Match\nService" as SM

participant "Donor Registry" as DR

skinparam SequenceMessageAlign center

skinparam dpi 192

== Making Request ==
PR -[#dodgerblue]> DR : Send message

MC --> PR : 400 Bad Request (optional)
MC --> PR : 200 OK (possibly with warnings)

PR -> MC : Check not-picked up messages

MC -> PR : 200 OK - Array of messages not yet delivered

== Getting Response ==

DR -[#dodgerblue]> PR : Message response (ack, reject, warning) \nshould always include messageId of referring message