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

CodeDisplayDefinition
requested RequestedThe client has requested the subscription, and the server has not yet set it up.
active ActiveThe subscription is active.
error ErrorThe server has an error executing the notification.
off OffToo many errors have occurred or the subscription has expired.
 <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="A status code for the state of the Subscription."/> <caseSensitive value="true"/> <valueSet value="http://terminology.hl7.org/ValueSet/subscription-status-at-event"/> <content value="complete"/> <concept> <code value="requested"/> <display value="Requested"/> <definition value="The client has requested the subscription, and the server has not yet set it up."/> </concept> <concept> <code value="active"/> <display value="Active"/> <definition value="The subscription is active."/> </concept> <concept> <code value="error"/> <display value="Error"/> <definition value="The server has an error executing the notification."/> </concept> <concept> <code value="off"/> <display value="Off"/> <definition value="Too many errors have occurred or the subscription has expired."/> </concept> </CodeSystem>