many of you commented and emailed that you are not being able to purchase tanks after the micropatch from 25 March was implemented, checked around the forums and every language staff is saying that is connected to mod usage.*While this sounds like a very standard answer to give it could be very well the truth this time, I bought a tank*the other night without issues.
Erase mods, if problem persists try to run the Game in Safe mode. If any of these helped let me know.