What we have learned running a pool of numbers that receives verification codes all day. Written for people who hit a problem and want the actual reason, not a list of generic tips.
The six digits, where they come from, why they expire so fast, and why security people keep saying SMS is the weakest way to receive them.
7 min read
Sorted by how often each one is the real cause, starting with the one that accounts for most failures on services like ours.
8 min read
Canadian numbering, why +1 does not mean the message will be treated as American, and what Canadian carriers filter.
6 min read
What the 07 prefix actually signals, how Ofcom rules shape what a virtual UK number can do, and where they get rejected.
6 min read
For developers. Why polling an inbox in a test suite is a trap, and what to assert on instead.
9 min read
Four ways to get a second number, what each one costs, and the one question that decides which you need.
7 min read
The FAQ answers the questions we get most often in a paragraph each. For the webhook API, see the developer documentation.