--- title: Message Header Elements slug: electronic-prior-auth/guide/message-header-elements docTags: createdAt: 2026-06-18T17:59:41.887Z --- | **Element** | **Code** | **Comments** | | -------------------------- | ------------ | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | To | mandatory  | The identification of the intended receiver of the message.
This field contains the identification number of the recipient.
For all PAInitiationRequests, this field contains EPAINI. For all subsequent Request messages, it will contain the Participant ID of the PBM/payer/third-party processor.
For Response messages, this field contains the SPI of the provider vendor. | | @Qualifier | conditional  | business rule 
If the To field is sent, then the Qualifier must also be sent.
Values:
**D** = Prescriber ID (Used for SPI)
**PY** = Payer (PBM/payer or third-party processor Participant ID)
**ZZZ** = Mutually Defined (used when sending to EPAINI) | | From | mandatory  | The identification of the sender of the message.
This field contains the identification number of the sender.
This field contains the SPI (Surescripts Provider ID) of the provider vendor, the Participant ID of the PBM/payer or third-party processor, or EPAINI. | | @Qualifier | conditional  | business rule 
If the From field is sent, then the Qualifier must also be sent.
Values:
**D** = Prescriber ID (Used for SPI)
**PY** = Payer (PBM/payer or third-party processor Participant ID)
**ZZZ** = Mutually Defined (only used when Surescripts is responding from EPAINI) | | MessageID | mandatory  | The sender should ensure the combination of the From and MessageID elements is unique for at least 18 months. Surescripts recommends an unformatted Globally Unique Identifier (GUID). | | RelatesToMessageID | conditional  | Relates to Message ID is required by Surescripts and usage details are further illustrated in the [Message Linkage](docId\:vJFKDx_T-WeUCpHv8wFh6) section. This field is the MessageID of the most recent and relevant message in the workflow, including outside of only ePA conversational messaging.
This is required for PAInitiationRequest, PAInitiationResponse, PARequest, PAResponse, PAAppealRequest, PAAppealResponse, PACancelRequest, PACancelResponse, Error, Verify, and Status. | | SentTime | mandatory  | Date of the transmission. Please see [UTC Time Format](docId\:a09JtnCxqtaJ1lqXdSeDW) section. | | SenderSoftware | mandatory  | Identifies the entity responsible that generated the message. Contains the software vendor name, product, and version/release.
These fields were previously blocked by Surescripts when passing the message on to the receiver. They will now be passed on to the receiver. | | SenderSoftwareDeveloper | mandatory  | Identifies the entity responsible for the software that generated the message. The developer may be a software vendor or, if the software was developed "in-house", the developer is the entity actually sending the message (e.g., a chain). The value transmitted is determined by the Sender Software Developer. | | SenderSoftwareProduct | mandatory  | The text field that identifies the software developer’s product, as determined by the software developer. | | SoftwareVersionRelease | mandatory  | The text field that identifies the version and release of the software product, as determined by the software developer. | | TestMessage | conditional  | When sent, allowable values must match platform that message is being sent to.
Values:
**1** = Test (Required in staging environment)
All other values = Live (Production)
Surescripts does not recommend sending this field within the production environment. | | Message Indicator Flag | conditional  | Not applicable to prior authorization transactions. | | ISA13 | conditional  | This is the Interchange Control Number ISA13 value from the Eligibility response X12 271 transaction. |