sproof Fastlane: Collecting Signatures (API)

Hello developer,

we are pleased to introduce the integration of the Fastlane functionality from sproof sign.

Imagine your recipients could sign documents on their mobile devices with just a few clicks, without having to navigate a complicated process. That's exactly what Fastlane enables. This feature was specifically designed for use cases that require fast and seamless signature processes, especially on mobile devices.

Fastlane offers a guided, step-by-step flow that greatly increases efficiency and user-friendliness for your recipients. You can customize and configure the entire signature process by creating a Fastlane profile.

To use Fastlane, this feature must be enabled in your user plan.

This guide walks you through creating a Fastlane profile, sending a signature request with the Fastlane option enabled via API, and then querying the status of that request.

Step 1: Create a Fastlane profile:

To configure the screens to be shown during the signature process (welcome, document, provider, sign, end) and other properties individually to adapt the user experience optimally to your needs, in this step we create a Fastlane profile.

API call: POST https://sign.sproof.com/api/v1/fastlane?token={{token}}

Documentation: Fastlane Profiles

{
  "name": "Document Signing for HR",
  "screens": {
    "welcome": {
      "enabled": true,
      "title": "Welcome to Fastlane",
      "description": "This is a test.",
      "icon": true,
      "showDocumentBtn": true
    },
    "end": {
      "enabled": true,
      "title": "",
      "description": "",
      "icon": true,
      "helpText": true,
      "shareDocumentBtn": true,
      "showDownloadDocBtn": true
    }
  },
  "successEmail": {
    "subject": "SUBJECT",
    "title": "THIS IS THE CUSTOM TITLE",
    "text": "CUSTOM TEXT THAT IS ADDED IN THE FASTLANE",
    "sendEmail": true
  }
}

The response to this call contains the id of the Fastlane profile (in this example b1f15495-8b48-4317-b279-1afee0d96e6e), which we need in the next step.

{
    "id": "b1f15495-8b48-4317-b279-1afee0d96e6e",
    "name": "Document Signing for HR",
    "createdAt": "2025-08-05T05:11:43.293Z",
  // ... further profile information
}

Step 2: Create a signature request with the Fastlane profile

Now we create the actual signature request and use the id of the profile from step 1 to apply the Fastlane profile. To invite recipients via Fastlane, the useFastlane flag must be set to true.

API call: POST https://sign.sproof.com/api/v1/documents/signature

Documentation: Signature Requests

{
  "token": "{{token}}",
  "inviteData": {
    "sender": {
      "email": "{{email}}",
      "firstName": "sproof",
      "lastName": "Sender"
    },
    "recipients": [
      {
        "email": "max.mustermann@sproof.com",
        "firstName": "Max",
        "lastName": "Mustermann"
      }
    ],
    "subject": "This is the subject of the email to the recipient/s",
    "message": "This is a custom message sent in the email"
  },
  "envelopeData": {
    "documentDataArray": [
      {
        "data": "{{pdf_im_base64_format}}",
        "fileName": "wichtiger_vertrag.pdf",
        "recipientDetails": {
          "max.mustermann@sproof.com": {
            "role": "signer",
            "signaturePositions": [
              {"page": 0, "x": 0.57489, "y": 0.8455, "width": 0.35, "height": 0.1}
            ]
          }
        }
      }
    ],
    "useFastlane": true,
    "fastlaneProfileId": "b1f15495-8b48-4317-b279-1afee0d96e6e"
  }
}

• Replace {{token}} with your API token.

• {{email}} is the sender's email address (must be a member of the same plan).

• {{pdf_im_base64_format}} should contain the Base64-encoded PDF document you want to have signed.

• subject: Here you can choose the subject of the email sent to the recipient(s).

• messages: Here you can provide a custom message for the email.

• useFastlane: true to invite the recipient(s) via Fastlane.

• fastlaneProfileId: Insert the id of your Fastlane profile created in step 1 here.

The response to this call includes, among other things, a member object (= sender) and a members array listing the invited recipient(s). We use the sender's memberId (member.id) in step 4 to query the current status of the signature request.

Step 3: The recipient is now notified by email

In our example, Max Mustermann receives an invitation to sign.

And is guided through the screens we previously configured to place his signature.

Step 4: Query the current status of the signature request

With get request status you can track the progress of a signature request. For this you only need to provide the token and the memberId of the sender to ensure an unambiguous assignment of the request for the respective document. The endpoint returns a JSON object that contains detailed information about the document and its status.

Endpoint: GET https://sign.sproof.com/api/v1/documents/{{memberId}}?token={{token}}

• Replace {{memberId}} with the id of the sender that you received in the response from step 2 under member.id.

• Replace {{token}} again with your API token.

We hope this example helps you get started with your integration!

If you have any questions, we are happy to assist you.

Last updated: August 21, 2026