SMS from One Country to Another Not Working

[HR-Sensible]

We have a team in the Philippines and Australia, but the team in the Philippines is unable to send text messages from their Australian phone numbers. 

Why is this? 

How do we fix this? 

They're able to receive calls on the Aussie number but can't send text messages. 

[sparrow]

I suspect this has something to do with it. When you hover over the question mark in the circle next to allow international SMS, you'll see additional details.