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FILTER vs. OTP verification
An OTP asks the customer to prove the number works. FILTER just checks.
OTP verification is the default most teams reach for, and for good reason — it's simple to wire up and it's genuinely reliable when the customer cooperates. The difference is when you find out something is wrong: OTP tells you after the customer has already been asked to do something. FILTER tells you before you ever contact them.
| FILTER | OTP verification | |
|---|---|---|
| When you learn the number is bad | Before you contact the customer | After they fail to receive or enter the code |
| Customer friction | None — invisible to the customer | Requires an extra step, and drop-off at that step is real |
| Cost per check | One credit, regardless of outcome | One SMS per attempt, plus retries |
| Proves the customer currently controls the number | No — it checks the line, not possession | Yes — this is what OTP is actually good at |
| Best for | Filtering leads and orders before you act on them | Confirming account ownership at login or password reset |
If you need to prove someone currently holds a specific phone, OTP is the right tool and FILTER doesn't replace it. If you need to filter thousands of leads or orders before spending money on them, an OTP flow is the wrong tool for that job — the friction and cost compound at volume in a way a single API check doesn't.