I’ve ended up answering this question on this topic (I think ), but for reference to other readers, I’ll repost it here.
Considering a template with a dropdown define as such:
{
"document_tag_id": "ext_id_dropdown",
"id": "b7fc6ae3-5a64-4746-a266-408f2fa550c5",
"type": "dropdown",
"text_value": null,
"is_required": true,
"coordinates": {
"x": 0.157528641571195,
"y": 0.5615431436187784
},
"dimensions": {
"width": 0.2618657937806874,
"height": 0.021464646464646464
},
"date_value": null,
"page_index": 0,
"checkbox_value": null,
"document_id": "16966a7e-13a6-447a-a465-dd87e28c2565",
"content_type": "dropdown",
"dropdown_choices": [
"Dropdown A",
"Dropdown B",
"Dropdown C"
],
"group_id": null,
"label": "drop_down"
},
To pre select a dropdown entry in the creation of a sign request:
{
"document_tag_id": "ext_id_dropdown",
"text_value": "Dropdown B"
}