[API Error] 400 "variables is invalid" for Template ID ea934e5fc17249ac954bd22b83f6788e

Hello everyone,

I'm on the HeyGen Pro plan and trying to generate a video via the API. My template ID is ea934e5fc17249ac954bd22b83f6788e.

Whenever I send a POST request to:

POST https://api.heygen.com/v2/template/ea934e5fc17249ac954bd22b83f6788e/generate

I get a 400 Bad Request with:

{"data":null,"error":{"code":"invalid_parameter","message":"variables is invalid: field required"}}

Here’s my JSON body:

{
  "caption": false,
  "callback_id": "myCallback",
  "title": "Test Video",
  "dimension": {
    "width": 1280,
    "height": 720
  },
  "include_gif": false,
  "enable_sharing": false,
  "template": {
    "template_id": "ea934e5fc17249ac954bd22b83f6788e",
    "variables": {
      "text_layers": {
        "Categorytext": {
          "name": "Categorytext",
          "type": "text",
          "properties": {
            "text": "Sample Category"
          }
        },
        "Headlinetext": {
          "name": "Headlinetext",
          "type": "text",
          "properties": {
            "text": "Sample Headline"
          }
        },
        "Subtitletext": {
          "name": "Subtitletext",
          "type": "text",
          "properties": {
            "text": "Sample Subtitle"
          }
        }
      },
      "image_layers": {
        "Image_1st": {
          "name": "Image_1st",
          "type": "image",
          "properties": {
            "url": "https://example.com/image1.jpg"
          }
        },
        "Image_2nd": {
          "name": "Image_2nd",
          "type": "image",
          "properties": {
            "url": "https://example.com/image2.jpg"
          }
        },
        "Image_3rd": {
          "name": "Image_3rd",
          "type": "image",
          "properties": {
            "url": "https://example.com/image3.jpg"
          }
        }
      }
    }
  }
}

I've confirmed the placeholders match exactly what's in the template and removed any unused ones (like Script or audio layers). I also sanitized text to remove special characters, but I still receive the same error.

Is there possibly a hidden placeholder or a required layer I'm missing? Any advice is greatly appreciated.

Additional Info:

Plan: Pro
Template ID: ea934e5fc17249ac954bd22b83f6788e
n8n version: 1.66.0 (if relevant)
Thank you in advance!