If you have subscribed to SMS sending, and to ensure that SMS sending works as expected, make sure to format mobile phone numbers in the E.164 international format (with a '+' and country code).
Here are a few examples:
| Country | Local | E.164 |
|---|---|---|
| USA | 415 555 2671 | +14155552671 |
| UK | 020 7183 8750 | +442071838750 |
| China | 021 6309 5246 | +862163095246 |
| Australia | (08) 9287 8230 | +61892878230 |