Are you looking to get an official certification or just want to be good at it?
If you want to be get an official certification, then you need to find out who issues those and check with them for requirements.
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To add onto CharlieBrown, before you can get certified in VM, you have to attend one of their classes. You cannot just purchase a voucher and take the test.
After you take the first class, they give you a voucher for the certification exam, it is part of the cost. After that, you can go for other certs in VM without taking anymore classes.