Some Galaxy S21, S21 + and S21 Ultra units are not compatible with MST for Samsung Pay. It seems that the availability of the resource varies according to the country – some understand, others do not, and not in a way that makes much sense.
The MST allows the phone to work with point of sale terminals that only support traditional magnetic stripe cards. This is important in the USA, where these terminals are quite common, except in regions where NFC terminals are abundant.
Unfortunately, the S21 phones sold in the United States are in the group without MST. Phones sold in the UK have. Is it because of the different chipsets (Snapdragon in the USA, Exynos in Europe)?
It does not seem to be the case. The specifications of the press releases from France, Italy and Germany do not mention the MST. The Dutch lists the MST, as well as the Polish, Russian and Indian press releases.
Here is Samsung’s statement on the matter when questioned by XDA:
Due to the rapid adoption of near-field communication (NFC) technology by consumers and businesses, starting with devices launched in 2021, Samsung Pay will focus its support on NFC transactions across the Galaxy portfolio. Although future devices no longer include magnetic stripe technology (MST), customers with previous and compatible Galaxy devices will be able to continue using Samsung Pay, including MST.
The MST was introduced with the Galaxy S6 in 2015 and has been a staple of the latest generation Galaxys ever since. Now he has a foot outside the door.
Source