Stale lookup cache routes OTP wrong and wastes prepaid

Lookup is a routing signal with a timestamp, not a permanent tattoo on the number. A cached line-type — mobile, VoIP, landline, unknown — that outlives the number’s real path will send OTP SMS into a dead range, skip a voice fallback a real mobile needed, or add friction to a customer who ported yesterday. You still pay the lookup row and the wasted segment.

IOSOR packages lookup beside messaging in one white-label prepaid wallet. Catalog live means the check is ready; in setup is not a production gate you cache around. Near USD 1,000+ monthly usage, cache age and wasted OTP segments become commercial review material. No platform subscription to keep checks available.

Stale line-type is a routing bug with a wallet cost

Yesterday’s “mobile” is today’s VoIP range, or a port the other way. Product still fires SMS. DLR comes back undelivered or the user never sees the code. Finance sees a lookup debit plus an SMS debit for zero conversion — stale cache, not “lookup ROI.” Contrast VoIP vs mobile before OTP.

Cache is allowed. Unbounded cache trusts last month’s network. If the UI cannot show looked-up-at next to line-type, ops cannot debug a corridor.

Cache TTL is a product decision, not a convenience

TTL is not “as long as the database likes.

• Short TTL (minutes–hours) on signup, promo, or any path where VoIP abuse or ports are common.
• Medium TTL on returning users where the number is bound to a verified account — still refresh on risk signals.
• Do not cache “unknown” as if it were mobile. Unknown is a decision to check again or fail closed.

A global 30-day cache looks cheap until one recycled range burns a week of OTP. Publish hit rate and age buckets, not only “lookup calls saved.” Pair with lookup ROI on the OTP path so finance sees when a cache “saving” is a wasted SMS.

VoIP versus mobile: when a refresh is mandatory

Refresh before send when any of these fire:

1. Line-type is VoIP, unknown, or older than the corridor TTL.
2. Multiple OTP requests against the same number or range in a short window.
3. The user changed the number on the account.
4. Last OTP on this number expired or came back undelivered.
5. Destination class is expensive enough that a wrong SMS costs more than a fresh check.

Landline still should not receive SMS. VoIP is a routing signal, not a fraud verdict. Blanket bans block real soft-phone customers; stale “mobile” labels do the opposite. When a check belongs in budget: lookup reconnaissance before send.

When a fresh lookup pays for itself

Pay for a live check when avoided SMS + retries + tickets exceed the lookup debit, including the cost of being wrong on a stale hit.

Red flags

• Line-type with no freshness or confidence
• “Unknown” cached as mobile
• Lookup sold as 100% delivery
• No wallet line for checks separate from SMS
• Blanket VoIP block with no live refresh path
• OTP retries on undelivered without a new lookup
• Catalog in setup while product caches empty results

Start with IOSOR

Audit your current lookup caching rules in the IOSOR console to set corridor-specific TTL caps for line-type data. Gate high-risk signup paths with forced live refreshes whenever a cached record marks a number as unknown or VoIP. Configure webhook triggers so that failed DLRs on cached numbers instantly invalidate the saved line-type and mandate a fresh lookup before the next OTP retry.

IOSOR takeaway

Stale lookup caches turn valid OTP attempts into silent delivery failures and double debits across your prepaid wallet. Caching a number as mobile indefinitely ignores active ports and range reassignments, forcing your system to dispatch expensive SMS down dead or unsupported channels.