as an STT user, I need the error message related to the header update indicator clarified

[ADPennington]

Description:

As noted here, when #2963 merges, this will introduce an item number into the error message related to header update indicator, which is currently the most common error message that STTs receive.

It looks like the following (when the update indicator is N, for example): HEADER Item 10 (update indicator): N does not match D.

• Header is not associated with an item number.
• STTs also seem confused about the current error message in prod (when the update indicator is N, for example): HEADER update indicator: N does not match D.

Acceptance Criteria: Create a list of functional outcomes that must be achieved to complete this issue

• [ ] Error message for header update indicator does not include item number
• [ ] Error message for header update indicator matches language spec from UX team
• [ ] Testing Checklist has been run and all tests pass
• [ ] README is updated, if necessary

Tasks: Create a list of granular, specific work items that must be completed to deliver the desired outcomes of this issue

• [ ] UX team provides language spec for header update indicator error message
• [ ] error message updated to include new language and remove item number
• [ ] Run Testing Checklist and confirm all tests pass

Notes: Add additional useful information, such as related issues and functionality that isn't covered by this specific issue, and other considerations that will be helpful for anyone reading this

• from @jtimpe:

the change is relatively easy:

Field(
item="10",
name="update",
friendly_name="update indicator",
type="string",
startIndex=22,
endIndex=23,
required=True,
validators=[validators.matches("D")],
),

for our update indicator field, the matches validator can take a second argument error_func, similar to how startsWith works in the preparsing validators

validators.startsWith(
"HEADER",
lambda value: f"Your file does not begin with a {value} record."
)

that would let us hard code the message for the one specific case

Supporting Documentation: Please include any relevant log snippets/files/screen shots

• 2818

• 2963

Open Questions: Please include any questions or decisions that must be made before beginning work or to confidently call this issue complete

• @reitermb @victoriaatraft can you provide guidance on the error message for the error message referenced in this ticket?