Welcome to the community!
We'd love to help see what causing error message with the international SMS and get to the bottom of this. To better understand the situation, PM us your account details (Customer ID / Mobile number)
In case you need a reference: How do I private message (PM) in the community
Hi @Edwin ,
Thanks for sending me your details. We're able to locate the account and confirmed that International SMS is not included to your Mobile Plan of T4G.
You may visit this link. https://www.tpg.com.au/mobile#mobile-call-rates_ and click the $19.99 Mobile Plan Tab.
You may Top-up of minimum $10.00 to send international SMS.
SMS to International Mobiles 50¢ per message (max 160 characters)
Let me know should you require further assistance.