My T-Mobile ONE plan still has the 30 day, $50 15Gb upgrade available if that is what you are referring to? Here is a copy & paste from the website.

"15GB International Pass

$50.00 Includes up to 15GB of high-speed data, including Mobile Hotspot, PLUS unlimited calling for up to 30 days in over 210 destinations. Speeds & coverage vary based on device and country. Note: Once you use all your high-speed data, you will continue to have unlimited calling and data for the full 30 days but may experience slower data speeds. If you use all your high-speed data and purchase a NEW pass before the expiration of the first one, your second pass will begin immediately. Your original pass and any remaining benefits will expire when you activate the new pass."