Docs
Templates
Use stored Handlebars templates when the same layout will render many times with different data. Create and publish a draft, then pass templateId plus templateData to POST /v1/pdf. One-off HTML still belongs on POST /v1/pdf with html.
Create a draft, publish it, then send templateId plus templateData. Same API key. HTML is UTF-8 JSON, not Base64. templateId may be the UUID or slug.