You can receive the error for the following reasons:
The phone number is blocked by a carrier as spam.
The phone is blocking SMS.
The mobile number isn't valid.
The phone is temporarily out of the coverage area.
The phone is in a roaming network.
If you did not receive your one-time password (OTP) via email, please first check your Spam, Junk, or Promotions folder, as automated emails can sometimes be filtered there.
Please contact your phone carrier to discuss the possible reasons.