Microsoft Learn - Xamarin + Twilio

I ran through "Share your location as a text message using Azure Functions and Twilio" at Microsoft Learn to understand Xamarin. It looks not just about Xamarin, and you cannot learn the whole picture of Xamarin from this, but it is a good practice if you are not familiar with client apps.They system figure is below.

Point 1
In Twilio, phone numbers in some countries do not support SMS. Japan not. I tried many times but it has errors. So, I finally changed the phone number to US one with SMS.

Point 2
Twilio cannot send SMS message to unverified phone number. So, you should verify your own phone number on Twilio, otherwise it has errors.

Point 3
If you are in Japan, there are two choices for Twilio. https://www.twilio.com and https://twilio.kddi-web.com/. I had thought they are the same website but just language is different. But the truth is they are different site, and you can create accounts for both sites with the same email address.