Host a single HTTPS endpoint on your server. The signing app receives its URL as the request_url query parameter and calls it with GET, HEAD, and POST.
Content-Type: application/pdf and header X-Sigilla-IoSigno-Type: request. We do not validate magic bytes or parse the PDF on HEAD.303 on success with a Location header containing the URL the signer must be redirected to after the signature succeeds, or 400 with a plain-text error message shown verbatim to the signer. We may send an optional Accept-Language header to help you localize the message — do not assume it is always present.That's the entire integration. The signing app accepts any endpoint you host yourself.