This code system http://terminology.hl7.org/CodeSystem/subscription-tag defines the following codes:

CodeDisplayDefinition
queued QueuedThe message has been queued for processing on a destination systems.
delivered DeliveredThe message has been delivered to its intended recipient.
 <status value="draft"/> <experimental value="false"/> <date value="2020-04-09T21:10:28+00:00"/> <publisher value="HL7 (FHIR Project)"/> <contact> <telecom> <system value="url"/> <value value="http://hl7.org/fhir"/> </telecom> <telecom> <system value="email"/> <value value="fhir@lists.hl7.org"/> </telecom> </contact> <description value="Tags to put on a resource after subscriptions have been sent."/> <caseSensitive value="true"/> <valueSet value="http://terminology.hl7.org/ValueSet/subscription-tag"/> <content value="complete"/> <concept> <code value="queued"/> <display value="Queued"/> <definition value="The message has been queued for processing on a destination systems."/> </concept> <concept> <code value="delivered"/> <display value="Delivered"/> <definition value="The message has been delivered to its intended recipient."/> </concept> </CodeSystem>