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Overview

The Sign API provides instant biometric signing for lightweight legal use cases. Perfect for terms of service, privacy policies, data attestations, and other agreements that require legal binding but don’t need document attachments.

Use Sign API For

Terms of service agreements
Privacy policy acknowledgments
Data honesty attestations
Simple consent forms
Compliance acknowledgments
Lightweight agreements

Use Messaging API For

  • Document signing with attachments
  • Contracts and legal documents
  • Multi-party signing workflows
  • High-stakes legal agreements
  • Document version control
Learn about Messaging API →

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How It Works

The Sign API provides instant biometric signing through a simple webhook-based flow. Users scan a QR code (desktop) or open the UIP app directly (mobile), review the document text, and sign with their biometric.

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Request Parameters

webhook_url (required)

Type: string (URL format)URL to receive signing results. Must be HTTPS in production.Your webhook will receive a POST request when the user completes or declines the signature.
Type: stringTitle or name of what the user is signing.Example: "Terms of Service v2.1", "Privacy Policy", "Medical Information Accuracy Attestation"Best Practice: Include version numbers for policies
Type: stringFull text content that the user will read and sign.Requirements:
  • Must be complete and readable
  • User will see this exact text in their UIP app
  • Plain text or markdown supported
  • No HTML tags
Best Practice: Keep concise but complete. Users should be able to read it in under 2 minutes.
Type: objectAdditional data to associate with the signature for your records.Common fields:
  • version: Document version number
  • user_ip: IP address of user
  • timestamp: When request was initiated
  • form_id: Internal form identifier
  • session_info: Additional session context
Note: Metadata is returned in webhook and audit trail

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Request Examples

Use Case: User agreeing to updated terms of serviceThe request includes the full terms text and version information.Webhook Response: Includes signature proof and timestamp for compliance records.

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Response

After creating a signature request, you’ll receive a session ID and QR code (for desktop flows). The QR code expires after 5 minutes. Users scan the code with their UIP app, review the document, and sign with their biometric.

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Common Use Cases

Perfect for:
  • Terms of service updates
  • Privacy policy acknowledgments
  • Code of conduct agreements
  • Compliance training completion
  • Safety protocol acknowledgments
Benefits:
  • Legally binding signatures
  • Audit trail for compliance
  • Version tracking in metadata
  • Permanent verification records

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Best Practices

Keep It Concise

Users should be able to read the document in under 2 minutes. For longer documents, use the Messaging API with PDF attachments.

Version Everything

Always include version numbers in document_title and metadata. Essential for tracking policy changes.

Store Audit References

Save the audit_reference_id from webhook responses. This is your permanent proof of signature.

Handle Declines Gracefully

User declines are normal. Provide clear messaging and easy retry options.

Use Metadata

Include version, IP address, timestamp, and other context. Helpful for compliance and debugging.

Test Thoroughly

Use your $5 signup credit to test with various document lengths, special characters, and edge cases.

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Sign API vs Messaging API

When to Use Sign API

Use Sign API when:
  • Signing terms, policies, or simple agreements
  • No document attachment needed
  • Text-based content under ~2,000 words
  • Fast, lightweight signing required (5-minute window)
  • Immediate response needed
  • Version tracking in metadata is sufficient
Key characteristic: Ultra-lightweight - users have 5 minutes to sign when initialized, then it expires. Perfect for instant agreements that require immediate confirmation.Pricing: $0.03 per signature
Use Messaging API when:
  • Document attachment required (PDF contracts, etc.)
  • Multi-page legal documents
  • Document version control needed
  • High-stakes legal agreements
  • File must be permanently stored for audit
  • Users need time to review (available up to 3 months)
Key characteristic: Long-term - messages stay in the user’s account for up to 3 months, giving them ample time to review and sign.Pricing: $0.10 per message with attachmentLearn more about Messaging API
Legally Binding: Signatures via Sign API are legally binding under the ESIGN Act (US) and eIDAS regulation (EU). Each signature includes government-verified identity, biometric authentication proof, cryptographic signature, immutable audit trail, and precise timestamp.

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Pricing

$0.03 per successful signature Only charged when users complete the signature. Failed attempts, cancellations, and expirations are not billed.

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Next Steps

Get API Keys

Start integrating UIP Sign API

API Reference

Complete API reference with request/response schemas

Messaging API

Learn about document signing with attachments