Text message error (Invalid phone number)

Would help if you could provide more context on what service you are using and what you have tried.

General, troubleshooting -- make sure that you are fitting the format of the field and including the correct country code.

Assuming a bit that you are working with PinPoint, make sure that the country your number is in is supported.
https://docs.aws.amazon.com/sms-voice/latest/userguide/phone-numbers-sms-by-country.html

Hope this helps!

Hello,

You can also use Phone Number Validate command to validate the number

it returns the following information:

- The phone number in E.164 format.
- The phone number type (such as mobile, landline, or VoIP).
- The city and country where the phone number is based.
- The service provider that's associated with the phone number. 

[+] https://docs.aws.amazon.com/pinpoint/latest/developerguide/validate-phone-numbers.html
[+] https://docs.aws.amazon.com/pinpoint/latest/apireference/phone-number-validate.html