This code system http://hl7.org/fhir/v2/0553 defines the following codes:

CodeDisplayComments
AAAuthorization request for inpatient admission
AICombined Authorization and Adjudication request
CACancel Authorization request
CGCancel Invoice Product/Service GroupCancel a specific Product/Service Group in an Invoice
CLCancel Invoice Product/Service Line ItemCancel a specific Product/Service Line Item in an Invoice
CNCancel InvoiceCan be used to reverse or cancel an invoice in progress or reverse a paid invoice. Receiver may only mark Invoice as cancelled, not purge records
CPCopy of Invoice
CQCoverage Register Query
EAAuthorization request for inpatient stay extension
OAOriginal Authorization
OROriginal Invoice
PAPre-Authorization
PDPre-Determination InvoiceCan be used to submit an invoice through a Payer's edit and adjudication engine to determine if the invoice will be paid - does not result in payment by Payer
RARe-AssessmentUsed on EHC^E04 only
RCReferral Pre-Authorization
RUReferral authorization
SASpecial Authorization