n8n SMS OTP Verify Workflow with Google Sheets Logging

Send and verify SMS OTPs with n8n—then log verified numbers to Google Sheets

This n8n automation workflow provides two webhook endpoints to send and verify 6-digit SMS one-time codes via SMS Vert Pro MCP, and automatically logs successfully verified phone numbers with timestamps into Google Sheets.

What this workflow does

• Exposes two webhook endpoints: /sms-otp/send to initiate an OTP SMS, and /sms-otp/verify to validate an OTP.
• Accepts POST requests and normalizes the submitted phone number.
• Validates inputs:
  • Checks the phone number against allowed country codes.
  • For verification, ensures the OTP is a 6-digit number.
• Returns proper error responses:
  • 400 for invalid requests.
  • 429 for send requests when a recent code already exists.
  • 401 when the OTP is wrong or expired.
• Sends OTPs by calling SMS Vert Pro MCP generate_otp and returns success or an error response.
• Verifies OTPs by calling SMS Vert Pro MCP verify_otp.
• Logs verification results: when the OTP is valid, it appends phone and verified_at to Google Sheets, then returns a 200 “verified” response.

Use cases

• Enable SMS OTP verification for an n8n-powered signup or account recovery flow.
• Validate customers’ phone numbers and maintain an audit trail in Google Sheets.
• Build a lightweight authentication layer for internal SaaS or onboarding processes.

Technical details

• Integrations: SMS Vert Pro MCP (API V2 token via Bearer Auth) and Google Sheets.
• n8n nodes used: webhook, if, set, code, google sheets, plus a sticky note for workflow documentation.
• Config you set: sender name, Google Sheet URL, default country code, and allowed country codes list.