Hi @tungnk !
I’d recommend first checking the How to collect SMS consent via API article to ensure that you have met all requirements.
In regards to the ‘Invalid or unsupported phone number’ error you are receiving, it is possible this is displayed because you may be unable to appropriately collect consent from a Vietnam phone number; even in testing. At the time of this post, Klaviyo is only enabled to collect SMS consent and send text messages in the United States, Canada, United Kingdom, and Australia. You can read more about that here.
You may choose to try testing with a phone number from one of the above listed countries to confirm if this is the issue.
Hope this is helpful!