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

LvlCodeDisplayDefinition
1invalid Invalid ContentContent invalid against the specification or a profile.
2  structure Structural IssueA structural issue in the content such as wrong namespace, unable to parse the content completely, invalid syntax, etc.
2  required Required element missingA required element is missing.
2  value Element value invalidAn element or header value is invalid.
2  invariant Validation rule failedA content validation rule failed - e.g. a schematron rule.
1security Security ProblemAn authentication/authorization/permissions issue of some kind.
2  login Login RequiredThe client needs to initiate an authentication process.
2  unknown Unknown UserThe user or system was not able to be authenticated (either there is no process, or the proferred token is unacceptable).
2  expired Session ExpiredUser session expired; a login may be required.
2  forbidden ForbiddenThe user does not have the rights to perform this action.
2  suppressed Information SuppressedSome information was not or might not have been returned due to business rules, consent or privacy rules, or access permission constraints. This information may be accessible through alternate processes.
1processing Processing FailureProcessing issues. These are expected to be final e.g. there is no point resubmitting the same content unchanged.
2  not-supported Content not supportedThe interaction, operation, resource or profile is not supported.
2  duplicate DuplicateAn attempt was made to create a duplicate record.
2  multiple-matches Multiple MatchesMultiple matching records were found when the operation required only one match.
2  not-found Not FoundThe reference provided was not found. In a pure RESTful environment, this would be an HTTP 404 error, but this code may be used where the content is not found further into the application architecture.
3    deleted DeletedThe reference pointed to content (usually a resource) that has been deleted.
2  too-long Content Too LongProvided content is too long (typically, this is a denial of service protection type of error).
2  code-invalid Invalid CodeThe code or system could not be understood, or it was not valid in the context of a particular ValueSet.code.
2  extension Unacceptable ExtensionAn extension was found that was not acceptable, could not be resolved, or a modifierExtension was not recognized.
2  too-costly Operation Too CostlyThe operation was stopped to protect server resources; e.g. a request for a value set expansion on all of SNOMED CT.
2  business-rule Business Rule ViolationThe content/operation failed to pass some business rule and so could not proceed.
2  conflict Edit Version ConflictContent could not be accepted because of an edit conflict (i.e. version aware updates). (In a pure RESTful environment, this would be an HTTP 409 error, but this code may be used where the conflict is discovered further into the application architecture.).
2  limited-filter Limited Filter ApplicationSome search filters might not have applied on all results. Data may have been included that does not meet all of the filters listed in the `self` `Bundle.link`.
1transient Transient IssueTransient processing issues. The system receiving the message may be able to resubmit the same content once an underlying issue is resolved.
2  lock-error Lock ErrorA resource/record locking failure (usually in an underlying database).
2  no-store No Store AvailableThe persistent store is unavailable; e.g. the database is down for maintenance or similar action, and the interaction or operation cannot be processed.
2  exception ExceptionAn unexpected internal error has occurred.
2  timeout TimeoutAn internal timeout has occurred.
2  incomplete Incomplete ResultsNot all data sources typically accessed could be reached or responded in time, so the returned information might not be complete (applies to search interactions and some operations).
2  throttled ThrottledThe system is not prepared to handle this request due to load management.
1informational Informational NoteA message unrelated to the processing success of the completed operation (examples of the latter include things like reminders of password expiry, system maintenance times, etc.).
1success Operation SuccessfulThe operation completed successfully.
<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="A code that describes the type of issue."/><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/issue-type"/><hierarchyMeaning value="is-a"/><content value="complete"/><concept><code value="invalid"/><display value="Invalid Content"/><definition value="Content invalid against the specification or a profile."/><concept><code value="structure"/><display value="Structural Issue"/><definition value="A structural issue in the content such as wrong namespace, unable to parse the content completely, invalid syntax, etc."/></concept><concept><code value="required"/><display value="Required element missing"/><definition value="A required element is missing."/></concept><concept><code value="value"/><display value="Element value invalid"/><definition value="An element or header value is invalid."/></concept><concept><code value="invariant"/><display value="Validation rule failed"/><definition value="A content validation rule failed - e.g. a schematron rule."/></concept></concept><concept><code value="security"/><display value="Security Problem"/><definition value="An authentication/authorization/permissions issue of some kind."/><concept><code value="login"/><display value="Login Required"/><definition value="The client needs to initiate an authentication process."/></concept><concept><code value="unknown"/><display value="Unknown User"/><definition value="The user or system was not able to be authenticated (either there is no process, or the proferred token is unacceptable)."/></concept><concept><code value="expired"/><display value="Session Expired"/><definition value="User session expired; a login may be required."/></concept><concept><code value="forbidden"/><display value="Forbidden"/><definition value="The user does not have the rights to perform this action."/></concept><concept><code value="suppressed"/><display value="Information Suppressed"/><definition value="Some information was not or might not have been returned due to business rules, consent or privacy rules, or access permission constraints. This information may be accessible through alternate processes."/></concept></concept><concept><code value="processing"/><display value="Processing Failure"/><definition value="Processing issues. These are expected to be final e.g. there is no point resubmitting the same content unchanged."/><concept><code value="not-supported"/><display value="Content not supported"/><definition value="The interaction, operation, resource or profile is not supported."/></concept><concept><code value="duplicate"/><display value="Duplicate"/><definition value="An attempt was made to create a duplicate record."/></concept><concept><code value="multiple-matches"/><display value="Multiple Matches"/><definition value="Multiple matching records were found when the operation required only one match."/></concept><concept><code value="not-found"/><display value="Not Found"/><definition value="The reference provided was not found. In a pure RESTful environment, this would be an HTTP 404 error, but this code may be used where the content is not found further into the application architecture."/><concept><code value="deleted"/><display value="Deleted"/><definition value="The reference pointed to content (usually a resource) that has been deleted."/></concept></concept><concept><code value="too-long"/><display value="Content Too Long"/><definition value="Provided content is too long (typically, this is a denial of service protection type of error)."/></concept><concept><code value="code-invalid"/><display value="Invalid Code"/><definition value="The code or system could not be understood, or it was not valid in the context of a particular ValueSet.code."/></concept><concept><code value="extension"/><display value="Unacceptable Extension"/><definition value="An extension was found that was not acceptable, could not be resolved, or a modifierExtension was not recognized."/></concept><concept><code value="too-costly"/><display value="Operation Too Costly"/><definition value="The operation was stopped to protect server resources; e.g. a request for a value set expansion on all of SNOMED CT."/></concept><concept><code value="business-rule"/><display value="Business Rule Violation"/><definition value="The content/operation failed to pass some business rule and so could not proceed."/></concept><concept><code value="conflict"/><display value="Edit Version Conflict"/><definition value="Content could not be accepted because of an edit conflict (i.e. version aware updates). (In a pure RESTful environment, this would be an HTTP 409 error, but this code may be used where the conflict is discovered further into the application architecture.)."/></concept><concept><code value="limited-filter"/><display value="Limited Filter Application"/><definition value="Some search filters might not have applied on all results. Data may have been included that does not meet all of the filters listed in the `self` `Bundle.link`."/></concept></concept><concept><code value="transient"/><display value="Transient Issue"/><definition value="Transient processing issues. The system receiving the message may be able to resubmit the same content once an underlying issue is resolved."/><concept><code value="lock-error"/><display value="Lock Error"/><definition value="A resource/record locking failure (usually in an underlying database)."/></concept><concept><code value="no-store"/><display value="No Store Available"/><definition value="The persistent store is unavailable; e.g. the database is down for maintenance or similar action, and the interaction or operation cannot be processed."/></concept><concept><code value="exception"/><display value="Exception"/><definition value="An unexpected internal error has occurred."/></concept><concept><code value="timeout"/><display value="Timeout"/><definition value="An internal timeout has occurred."/></concept><concept><code value="incomplete"/><display value="Incomplete Results"/><definition value="Not all data sources typically accessed could be reached or responded in time, so the returned information might not be complete (applies to search interactions and some operations)."/></concept><concept><code value="throttled"/><display value="Throttled"/><definition value="The system is not prepared to handle this request due to load management."/></concept></concept><concept><code value="informational"/><display value="Informational Note"/><definition value="A message unrelated to the processing success of the completed operation (examples of the latter include things like reminders of password expiry, system maintenance times, etc.)."/></concept><concept><code value="success"/><display value="Operation Successful"/><definition value="The operation completed successfully."/></concept></CodeSystem>