Why won't my mobile data work in some countries that are covered by my plan?

I have a moto g(7) power with an international T-Mobile plan that is supposed to allow me to use my phone in most countries around the world without needing to get new SIM cards. This works most of the time, but I've noticed a few countries not behaving correctly. What normally happens is that I'll get a text message from T-Mobile saying "Welcome to X country" and explaining that I have 5 gigs of high-speed data per month for that country. Then once the high-speed data runs out, I can still use unlimited low-speed data for the rest of the 30-day cycle. But for the countries where this doesn't work, I'll still get the text message that confirms the country is covered by my plan and I'll see that I have cell signal but when I open a browser or try to use messaging apps it says there's no Internet. Here is how it worked in Australia and New Zealand for example: - ✅ I get a text confirming that I have coverage in the country - ✅ The cell signal icon indicates a strong connection - ✅ I am able to use mobile data Here is how it's working in Fiji: - ✅ I get a text confirming that I have coverage in the country - ✅ The cell signal icon indicates a strong connection - ❌ I am not able to use mobile data Curiously, it seems that I am able to make phone calls and use SMS in Fiji, and I guess that's because those things are considered by phone plans to be different from mobile data. At first I thought maybe the problem was related to the 5 gigs of high-speed data being expired, but the problem still wasn't solved when the cycle ended and my high-speed data was renewed. I've tried using mobile data in Fiji both with and without high-speed data available and the problem is the same in both cases. T-Mobile customer support didn't seem to understand the problem unfortunately. Here are the troubleshooting steps they ran me through: 1. I reset the phone's network settings multiple times 1. I restarted the phone multiple times 1. I enabled international roaming None of that worked, of course. What is causing this problem, and is there anything I can do to fix it?