Working with letters via the API
Signing a letter through the API requires the practice to have API document signing enabled. Supplyingsigned_by and sign_date signs the letter only when the feature is turned on for the authoring practice; otherwise the request returns 400 and the letter is not signed. Requests that omit both fields are unaffected. Request that Elation enable it for the practice before building a workflow that signs. See Getting Help.
Field notes
tagsis documented separately. See The Document Tag Object.