Why don't OTP SMS come to Twilio number?

Question

Telephony

There are virtual numbers in Twilio. The goal is to receive SMS on them.

If you register, for example, in Proton mail, then temporary sms come to them.

But, if you change the Tinkoff number to one of my Wirth. numbers, or try to register in Yu-Money - not a fig, SMS does not come.

It turns out that the problem is that some RF operators do not deliver SMS to Twilio. Why?

Also, I tried to register in mail.ru, where after registration I should have received not an SMS, but a call to the Twilio number. And yes, he came.

How to treat?

Answer 1

No, it is not operators who send SMS to Twilio numbers. Applications and services do not use carrier networks for delivery. A2P (application-to-person) SMS does not work that way. Special integrations are used for this, the industry standard here is the SMPP protocol. As a rule, a specific service uses the services of some aggregator provider, to which it can send not only via SMPP, but also some other protocols. But in the future, the aggregator will send it via SMPP to either the end operator or another intermediary. It is simply unrealistic to integrate directly with all the operators in the world, there are dozens of them in Russia, hundreds in the USA, and how many in the whole world can no longer be counted. At the same time, it is never possible to know whether an SMS from a particular aggregator will go directly to the end operator or another intermediary (and in general it is impossible to know whether how many intermediaries will be on the way at all). At any stage of the chain, something can fail or not work reliably enough.
In addition, any stage of the chain can kill something at its own discretion: by texts, by numbers, by traffic source (with which system_id the message was received). After all, many countries have very complex rules and specifications. For example, in India, the maximum length of an alphanumeric name is 6 characters, and in Russia it is 11; in many countries or with individual operators, names must be pre-registered (they may be paid or free, may or may not require documentary evidence for a trademark). In some countries, mobile networks, in principle, do not support alphanumeric names (for example, in the USA), and there it is necessary to make a substitution for a digital one, which not every operator will miss in the future.
To a heap, some numbering capacities can be intentionally blocked as being used for targeted registration of accounts without a physical SIM card. For example, WhatsApp does not send SMS to some number rental services, even if the corresponding number has never been used.
It is impossible to refer to the successful circulation of SMS between ordinary subscriber devices, since ordinary SMS can travel over SS7, which is generally impossible for A2P SMS. Even if you find a hole in the SS7 network for money or on the darknet from some thread of an African operator, then there will be no delivery at all or its quality will be terrible (as far as I remember, for Russia 5 years ago, delivery did not exceed 40%, now it’s probably even worse) .
With questions about non-work, please contact the technical support of a particular service. Let them push their supplier, and he will push his partners along the chain.