This code system http://hl7.org/fhir/subscription-notification-type defines the following codes:

Code Display Definition
handshake Handshake The status was generated as part of the setup or verification of a communications channel.
heartbeat Heartbeat The status was generated to perform a heartbeat notification to the subscriber.
event-notification Event Notification The status was generated for an event to the subscriber.
query-status Query Status The status was generated in response to a status query/request.
query-event Query Event The status was generated in response to an event query/request.
<status value="active"/> <experimental value="false"/> <date value="2021-01-05T10:01:24+11:00"/> <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="The type of notification represented by the status message."/> <jurisdiction> <coding> <system value="http://unstats.un.org/unsd/methods/m49/m49.htm"/> <code value="001"/> <display value="World"/> </coding> </jurisdiction> <caseSensitive value="true"/> <valueSet value="http://hl7.org/fhir/ValueSet/subscription-notification-type"/> <content value="complete"/> <concept> <code value="handshake"/> <display value="Handshake"/> <definition value="The status was generated as part of the setup or verification of a communications channel."/> </concept> <concept> <code value="heartbeat"/> <display value="Heartbeat"/> <definition value="The status was generated to perform a heartbeat notification to the subscriber."/> </concept> <concept> <code value="event-notification"/> <display value="Event Notification"/> <definition value="The status was generated for an event to the subscriber."/> </concept> <concept> <code value="query-status"/> <display value="Query Status"/> <definition value="The status was generated in response to a status query/request."/> </concept> <concept> <code value="query-event"/> <display value="Query Event"/> <definition value="The status was generated in response to an event query/request."/> </concept> </CodeSystem>