eSignature with OTP (SES)
From: €0.09 + VAT
Integrate the electronic signature solution — compliant with eIDAS, ETSI standards, and fully aligned with GDPR — via API for just €0.09.
The Electronic Signature solution with OTP via API allows you to integrate an electronic signing process directly into your systems (CRM, ERP, SaaS, management platforms, portals, websites), eliminating the need to print, sign by hand, and scan documents. The signature is valid across Europe, compliant with regulatory standards (eIDAS, ETSI standards) and GDPR.
Thanks to an OTP (One-Time Password) mechanism, signer authentication is guaranteed — linking a specific user (via phone/email) to a precise signature on a document, with full traceability.
Electronic Signature Request
POST/EU-SES
The POST/EU-SES endpoint allows you to request the electronic signature service and obtain links to the platform where signers will complete the signing process.
At this stage, you must provide the document to be signed (URL or base64), the first and last name, an optional message, the authentication method, and where the signature will be placed (page and coordinates) for each signer. It is also possible to define:
- type of signature: "typed", i.e., digitalization of the name, and/or "drawn", i.e., drawn with a mouse
- OTP delivery method: email or SMS
- whether to allow users to edit their name, mobile number, and email for OTP
{
"signers": [
{
"name": "string",
"surname": "string",
"email": "[email protected]",
"mobile": "string",
"message": "string",
"authentication": [
"email"
],
"signatures": [
{
"page": 1,
"x": "331",
"y": "45",
"name": "string"
}
]
},
{
"name": "string",
"surname": "string",
"email": "test@emailcom",
"mobile": "string",
"message": "string",
"authentication": [
"email"
],
"signatures": [
{
"page": 1,
"x": "331",
"y": "45",
"name": "string"
}
]
}
],
"inputDocuments": "https://url.pdf.com",
"callback": {
"url": "https://www.mysite.it/callback.php"
},
"signatureMode": [
"typed",
"drawn"
],
"userEditableData": {
"name":"true",
"mobile":"true",
"email":"true"
}
}
During the request, you can also set a callback to be updated on the status change of the request.
EXAMPLE RESPONSE
POST/EU-SES
The response includes information such as:
- Request creation and update date,
- Request ID,
- Request status,
- Signer ID,
- URL for the signing process for each signer
At this stage, the link to the customizable platform (Web App) is returned, where each signer can view the document and complete the signing process using OTP authentication (defined during the request).
{
"data": {
"id": "6927055e66abe148eb0efc6b",
"errorNumber": null,
"errorMessage": null,
"updatedAt": "2025-11-26 13:49:18.879+00:00",
"createdAt": "2025-11-26 13:49:18.879+00:00",
"certificateType": "EU-SES",
"state": "WAIT_VALIDATION",
"signatureType": "pades",
...
},
"message": "Created",
"success": true,
"error": null
}The request ID will be essential for subsequent phases, particularly to check the request status and download the signed document.
Interface Customization
The simple electronic signature solution allows full customization, without limits, of the signing interface with company logos, colors, and redirect pages.
Specifically, it is possible to define:
- Sidebar background color
- Sidebar title and text color
- Footer background color
- Header title and text color
- Button text, background, and hover color
- Sign button text, background, and hover color
- Custom logo
- Hide sidebar, header, download button for validated or signed document
- Redirect URL after completing the signing process
- Redirect URL in case of signing process cancellation
Customization instructions must be passed as an option in the signing request payload and can be modified for each new signing process started.
If the interface is not customized, the default neutral interface without company logos will be used.
Document Verification
POST/verify
You can verify a signed document via the dedicated /verify endpoint. The payload must include the signed document in base64 and optionally the detached content, password for encrypted PDFs, and whether the verification is recursive or scheduled for a specific date.
Audit Trail
GET /signature/{id}/{actionType}
At the end of the signing procedure, you can request via API:
- Signed document
- Validated document
- Details
- Audit
The audit trail is the document containing all information leading to the successful completion of the signature. In case of disputes, this file allows every step of the procedure to be technically reproduced. The audit trail provides procedure data (ID, creation date, sending and expiration), signer data (name, surname, email, phone number, IP address), and signer authentication methods (authentication method, message sent, and validation time).
The audit trail is preserved in its original form for 10 years, as required by law, while the document is available for 3 months.
The electronic signature service is designed for:
- companies of all sizes (startups, SMEs, large enterprises)
- SaaS platforms, management software, CRM/ERP
- web portals handling contracts, quotes, orders, forms
- those looking to digitalize document processes and reduce paper usage
- those needing an integrated, secure, and traceable electronic signature system without leaving their software ecosystem
Do you need help?
Haven't found the answer you're looking for?
Fill in all the details, we will get back to you as soon as possible!
This service allows you to integrate the electronic signature solution via API into any type of platform and to dematerialize the signing of documents. Unlike traditional handwritten signatures, electronic signatures do not require any physical support, relying instead on digital processes that ensure the identity of the signer and the integrity of the document.
The OTP (One-Time Password) is a temporary password that serves to provide users with a high level of protection during the signing process.
Yes, the OTP electronic signature is recognized by EU law through the eIDAS regulation, ETSI, and is compliant with GDPR. Furthermore, at the end of the signing process, Openapi provides the option to request both the signed document and a copy of the audit trail, which contains all the information leading to the successful signing. In case of disputes, this file will allow for the technical reproduction of each step of the process. The audit trail contains data on the process (ID, creation date, sending and expiration), signers (name, surname, email, phone number, IP address), authentication methods of signers (authentication method, sent message, and validation time), and is stored in original form for 10 years as required by law.
On Openapi you can request the following types of signatures:
- Simple Electronic Signature with OTP (SES)
- Automatic Qualified Electronic Signature (QES)
- Automatic Qualified Electronic Signature with OTP (QES)
- Automatic Qualified Electronic Seal
In every signing process it is possible to brand the interface with the following customizations:
- Custom Logo
- Sidebar Background Color
- Sidebar Title and Text Color
- Footer Background Color
- Header Title and Text Color
- Button Text, Background and Hover Color
- Signature Button Text, Background and Hover Color
- Hide Sidebar, Header, Button to download validated or signed document
- Redirect URL after signing process completion
- Redirect URL in case of signing process cancellation
Yes, at the end of the signing procedure, you can request the signed document via API, in addition to the copy of the audit trail. The audit trail is the document containing all the information that led to the successful signing. In case of disputes, this file will allow for the technical reproduction of each step of the process. The audit trail contains data on the process (ID, creation date, sending and expiration), signers (name, surname, email, phone number, IP address), authentication methods of signers (authentication method, sent message, and validation time). As required by law, the audit trail is stored in original form for 10 years.
Our electronic signature solution complies with eIDAS/ETSI standards and GDPR, and offers greater legal robustness thanks to OTP and complete audit trail at the end of the signing process.
Simple electronic signature is particularly suitable for low-risk documents, such as:
- Home deliveries: signature to confirm receipt.
- Acceptance of notices: privacy, data processing, terms and conditions of online services.
- Registration for courses or events: when user consent is sufficient.
- Commercial documents: quotes, orders, order confirmations and transport documents (delivery notes).
- Internal orders and approvals: leave requests, expense reports, confirmation of business activities.
We recommend consulting your legal advisor to verify the specific legal requirements applicable to your company or sector.
The document will be available for 3 months, while the audit trail will be available for 10 years as per regulations.
The electronic signature service is simple and allows you to sign PDF documents remotely. You can have the same document signed by multiple people, on one or more pages.
The process is simple:
- Make a request via API indicating: the signers' data (first name, last name, email or mobile phone), the type of signature and the OTP verification method
- Receive the links to send to the signers
- The signers access the platform through the links and sign the document
- At the end, you can download the signed and validated document, together with the operations log (audit trail)
The eSignature with OTP is ideal for companies of all sizes and organizations that need to offer their clients a secure and certified signing solution that allows them to sign any digital document and dematerialize the signing of documents (e.g., pre-contracts, quotes, sales or rental contracts, and general documents).
The service is provided in real time.
The cost is charged based on the number of signatories and starts from €0.09 on subscription or €0.30 for single requests charged on credit.
Carbon free energy for Our Cloud 
Low CO2
© 2024 Openapi SpA, a single-member company, under the direction and control of Open Holding Srl.
Viale Filippo Tommaso Marinetti 221 - 00143 Rome - Business Register: 1378273, Share Capital: €50,000.00, VAT Number: IT12485671007, Recipient Code: 'USAL8PV' - Certified Email: 
Openapi is certified in: Quality System **UNI EN ISO 9001:2015** - Data Quality **ISO 25012:2014** - Security Management **ISO/IEC 27001:2022** - Geneder Equality According UNI PdR 125:2022
All prices are net of any VAT, stamp duty, registration fees, or other taxes that may be due. All logos listed on the portal are copyrighted and owned by their respective owners.
