Issues a POST to the Python/Flask backend at the bridge-supplied port, with Content-Type: application/json.
Content-Type: application/json
Body payload (already serialized) to send.
Path under the Flask root (no leading slash).
Callback invoked with the parsed JSON body.
Optional
Optional callback for fetch failures. Defaults to console.error.
console.error
Issues a POST to the Python/Flask backend at the bridge-supplied port, with
Content-Type: application/json.