This code system http://hl7.org/fhir/response-code defines the following codes:

Code Display Definition
ok OK The message was accepted and processed without error.
transient-error Transient Error Some internal unexpected error occurred - wait and try again. Note - this is usually used for things like database unavailable, which may be expected to resolve, though human intervention may be required.
fatal-error Fatal Error The message was rejected because of a problem with the content. There is no point in re-sending without change. The response narrative SHALL describe the issue.
<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 kind of response to a 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/response-code"/> <content value="complete"/> <concept> <code value="ok"/> <display value="OK"/> <definition value="The message was accepted and processed without error."/> </concept> <concept> <code value="transient-error"/> <display value="Transient Error"/> <definition value="Some internal unexpected error occurred - wait and try again. Note - this is usually used for things like database unavailable, which may be expected to resolve, though human intervention may be required."/> </concept> <concept> <code value="fatal-error"/> <display value="Fatal Error"/> <definition value="The message was rejected because of a problem with the content. There is no point in re-sending without change. The response narrative SHALL describe the issue."/> </concept> </CodeSystem>