This code system http://hl7.org/fhir/v2/0555 defines the following codes:

CodeDisplayComments
BKBlock
FNFinalFinal Invoice
FSFee for Service
GPGroup
INInformation OnlyPayee information not required for this Invoice Type
NPNon PatientInvoice without a patient; e.g. bulk invoicing for Pharmacy for a care facility.
PAPartialPartial Invoice
SLSalary
SSBy Session
SUSupplementalSupplemental Invoice