I'm struggling to translate my API Gateway Integration request into Terraform code, I'm trying to pass a multipart/form-data request to a Lambda for storage.

I've been able to set up the API gateway manually from scratch, but when I try the terraform I recieve an Internal server error and Cloudwatch tells me the gateway has been unable to transform the request.

Execution failed due to configuration error: Unable to transform request

The problem seems to be in the Integration request, because if I do the terraform deployment I can get the whole thing to work by changing the Integration Type in the UI to Lambda Proxy, changing it back again and adding re-adding the Mapping Template.

Terraform block for the Integration;

resource "aws_api_gateway_integration" "docuemnt-api-method-integration" {
  rest_api_id = aws_api_gateway_rest_api.document-api.id
  resource_id = aws_api_gateway_resource.document-resource.id
  http_method = aws_api_gateway_method.document-post-method.http_method
  type = "AWS"
  uri = aws_lambda_function.document_function.invoke_arn
  integration_http_method = "POST"
  passthrough_behavior = "WHEN_NO_TEMPLATES"
  request_templates = {
    "multipart/form-data" = file("${path.module}/mapping/mapping_template.json")
  }
}

The Mapping template

{
  "body":"$input.body",
  "content-type": "$util.escapeJavaScript($input.params().header.get('Content-Type'))"
}