Generate an image with FLUX.1 Fill [pro] using an input image and mask.

curl --request POST \
  --url https://api.us1.bfl.ai/v1/flux-pro-1.0-fill \
  --header 'Content-Type: application/json' \
  --header 'x-key: <api-key>' \
  --data '{
  "image": "<string>",
  "mask": "<string>",
  "prompt": "ein fantastisches bild",
  "steps": 50,
  "prompt_upsampling": true,
  "seed": 123,
  "guidance": 50.75,
  "output_format": "jpeg",
  "safety_tolerance": 2,
  "webhook_url": "<string>",
  "webhook_secret": "<string>"
}'

{
  "id": "<string>",
  "polling_url": "<string>"
}