> ## Documentation Index > Fetch the complete documentation index at: https://developer.sandbox.co.in/llms.txt > Use this file to discover all available pages before exploring further. # Verify OTP for CSI download > Verify the OTP to download the CSI file. Use the reference ID returned by [Generate OTP for CSI download](/api-reference/tds/compliance/download-csi/endpoints/generate_otp) and the OTP sent to the mobile number. On success, download the file using `data.csi_url`. An incorrect or expired OTP can return HTTP 200 with an error in `data.message`. Continue only when the response includes `data.csi_url`. ## OpenAPI ````yaml api-reference/tds/compliance/openapi.json POST /tds/compliance/csi/otp/verify openapi: 3.1.0 info: title: compliance description: >- Tax Deducted at Source (TDS) is an indirect method of collecting Income Tax. TDS is based on the principle of “Pay as you earn” which is beneficial for both the Government and the taxpayer. It is where a person making a payment of specified nature is liable to deduct tax at a prescribed rate. This ensures continuous revenue for the Government by way of Tax Deducted at the Source. The Payer making a payment is also responsible to deposit TDS with the Income Tax Department within a specified date and file a TDS Return. Once filed, the deposited amount will be shown in the Payee's Form 26AS which they can then use to claim tax credits when filing ITR. However, staying TDS compliant can be a hassle for businesses, as they are required to : 1. Deduct TDS from payments that are liable for TDS Deduction at an appropriate rate. 2. Deposit TDS to Government before the due date. 3. File TDS Returns on a Quarterly basis. 4. Issue a TDS Certificate by the deductor to the deductee. Organizations deducting TDS have to remain compliant with each of the steps. Failure to do so results in TDS Penalties by Authorities. Sandbox provides TDS Compliance APIs to help you automate end-to-end TDS compliance. version: 1.0.0 servers: - url: https://test-api.sandbox.co.in - url: https://api.sandbox.co.in security: [] tags: - name: TDS Compliance Check - name: Download CSI - name: FVU Generation - name: E-File TDS Return - name: TDS - name: TDS Certificate - name: TRACES Credentials paths: /tds/compliance/csi/otp/verify: post: tags: - Download CSI summary: Verify OTP for CSI download description: Verify the OTP to download the CSI file. parameters: - name: authorization in: header description: JWT access token required: true example: '' schema: type: string - name: x-api-key in: header description: API key for identification required: true example: '' schema: type: string - name: x-api-version in: header description: '' required: false example: '' schema: type: string requestBody: content: application/json: schema: type: object properties: '@entity': type: string enum: - in.co.sandbox.tds.compliance.deductors.csi.request reference_id: type: string description: >- The data.reference_id returned by Generate OTP for CSI download. otp: type: string description: >- OTP sent to the mobile number provided in the generation request. required: - '@entity' - reference_id - otp examples: 200 - Success: value: '@entity': in.co.sandbox.tds.compliance.deductors.csi.request reference_id: FOS005981930273 otp: '834201' summary: 200 - Success 200 Invalid OTP: value: '@entity': in.co.sandbox.tds.compliance.deductors.csi.request reference_id: FOS101212121212121 otp: '121212' summary: 200 Invalid OTP 200 OTP Expired: value: '@entity': in.co.sandbox.tds.compliance.deductors.csi.request reference_id: FOS101212121212121 otp: '121212' summary: 200 OTP Expired responses: '200': description: >- Check the response body for the result. HTTP 200 can also contain an application error in data.message. content: application/json: schema: type: object properties: timestamp: type: integer transaction_id: type: string data: type: object properties: '@entity': type: string tan: type: string from: type: integer to: type: integer reference_id: type: string description: Reference ID associated with the verified OTP request. csi_url: type: string description: >- Download the CSI file from this URL after successful verification. The example URL is illustrative. message: type: string description: >- Application error message when verification fails, such as an incorrect or expired OTP. code: type: integer examples: 200 - Success: summary: 200 - Success value: timestamp: 1731669721578 transaction_id: 8a0c097f-8e6d-4c11-8228-87d3c8cc44ce data: '@entity': in.co.sandbox.tds.compliance.deductors.csi.response tan: AHMA09719B from: 1722450600000 to: 1730313000000 reference_id: FOS005981930273 csi_url: https://example.com/challan.csi code: 200 200 Invalid OTP: summary: 200 Invalid OTP value: code: 200 timestamp: 1763362637000 transaction_id: e2b9145f-69d5-4bbe-a6de-be6fc08b426f data: '@entity': in.co.sandbox.tds.compliance.deductors.csi message: The OTP you have entered is incorrect. 200 OTP Expired: summary: 200 OTP Expired value: code: 200 timestamp: 1763362637000 transaction_id: e2b9145f-69d5-4bbe-a6de-be6fc08b426f data: '@entity': in.co.sandbox.tds.compliance.deductors.csi message: OTP expired headers: {} deprecated: false security: [] ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.