Proof of Holdings vs Sinch Verification
Sinch offers SMS, flash call, and voice verification for phone numbers. Proof of Holdings verifies any digital asset — phone, email, domain, wallet, social — with flat pricing and zero delivery failures.
Feature Comparison
| Feature | Proof of Holdings | Sinch Verification |
|---|---|---|
| Phone verification | Telegram, WhatsApp, SMS | SMS, Flash Call, Phone Call, Data |
| Email verification | Magic Link, OTP | |
| Domain verification | DNS TXT, HTTP, Admin Email, Auto-Verify | |
| Wallet verification | 8 chains (ETH, SOL, BTC, BNB, COSMOS, TRON, ADA, HBAR) | |
| Social verification | 12+ platforms (GitHub, Google, LinkedIn, X, etc.) | |
| Reverse OTP | ||
| Flash call verification | Android only, caller-ID based | |
| Cryptographic proof tokens | RS256 JWT, offline-verifiable | |
| Human-in-the-loop approvals | Telegram/WhatsApp with proof tokens | |
| MCP server for AI agents | 131 tools | MCP server available |
| Delivery failure rate | 0% (user-initiated) | 10-30% (SMS), lower with flash call |
| SIM-swap resistant | ||
| Free tier | 300 proofs/month |
Pricing
Cost per verification
Proof of Holdings
€0.0079/proof (any asset, any country)
Sinch Verification
Country-variable, not publicly listed (requires Sinch account to view rates)
International pricing
Proof of Holdings
Flat rate, same price worldwide
Sinch Verification
Varies by country: $0.05-0.50+ per SMS internationally
Free tier
Proof of Holdings
300 proofs/month
Sinch Verification
No free tier
Multi-asset pricing
Proof of Holdings
Same price for phone, email, domain, wallet, social
Sinch Verification
Phone only — no email, domain, wallet, or social
The Hidden Cost: Country-Variable Pricing
Sinch advertises $0.01-0.06 per verification request. But this is the platform fee only. On top of that, you pay SMS channel fees that vary dramatically by destination country.
An SMS to the US costs ~$0.01-0.06 depending on provider. To France, $0.08 (Plivo). To Netherlands, €0.08 (Infobip). To some countries, $0.20-0.50+. The advertised price and the real price are very different things.
Proof of Holdings charges €0.0079 per proof regardless of country or asset type. Phone verification to any country, email, domain, wallet, social — all the same flat rate. No country surcharges, no channel fees, no surprises.
Flash Call vs Reverse OTP
Sinch's flash call is a missed-call verification: the service calls the user's phone, the call auto-hangs-up, and the verification code is embedded in the caller ID. The user's phone reads it automatically.
Flash call is clever but limited: Android only (iOS blocks caller-ID reading), requires phone permission, and depends on carrier support. It doesn't work in all countries.
Proof of Holdings' Reverse OTP works on any device, any OS, any country where the user has Telegram, WhatsApp, or . The user sends a code to the service — 0% delivery failure, no carrier dependency, no OS restrictions.
Security & Proof Tokens
Both Sinch's SMS and flash call channels are vulnerable to SIM-swap attacks. If an attacker controls the phone number, they receive the SMS or flash call.
Proof of Holdings is immune to SIM-swap — Reverse OTP requires the user to send a message from their actual Telegram, WhatsApp, or account.
Every Proof of Holdings verification produces an RS256-signed JWT proof token verifiable offline. Sinch returns a verification status with no cryptographic attestation.
When to use Sinch Verification
- You want flash call verification for Android users (lower cost than SMS in some markets)
- Your use case is strictly phone-only verification
- You need Sinch's broader CPaaS platform (SMS, voice, video)
- Flash call carrier coverage is good in your target markets
When to use Proof of Holdings
- You need to verify more than phone numbers (email, domain, wallet, social)
- You want flat, predictable pricing with no country surcharges
- You need verification that works on any device and OS
- You want cryptographic proof tokens for every verification
- You need human-in-the-loop approvals for AI agents
- You operate internationally and want 0% delivery failure
Frequently Asked Questions
Ready to try Proof of Holdings?
300 free proofs per month. No credit card required.