The documentation on the Organization.identifier:payerid slice is vague on what we mean by "Payer ID" and I think it won't be clear to implementers new to the medical insurance industry exactly what ID to use. We should clarify that this is the 5 character payer ID typically used in EDI 837 claim transactions as the payer or receiver identification code, and sometimes also printed on plan member wallet cards. A single payer organization may have multiple Payer IDs; UnitedHealthcare has dozens. And we should update at least one of the Organization resource examples to include a Payer ID.

Availity has a convenient Payer List which shows the 5 character IDs for most payers. We can use that to look up some sample values.