Download a CSV template for a manual sending preset

Returns a CSV containing only a header row with every column accepted by the matching POST .../send endpoint, given the preset's contentable and the organization's configured metafields.

• Survey preset — always email,phone; adds patient_id when the survey has patient tracking enabled; adds language when the survey is configured for more than one language across its email / SMS messages; appends one column per available org-level metafield.
• Communication preset — single phone column.

The response is a CSV (Content-Type: text/csv) with a Content-Disposition: attachment; filename="<preset>-template.csv" header.