This is a very general sentence: "the best paid math journals".
There are many paid math scientific journals in the world, and in general, there are many journals whose scientific value and prestige are accepted by reputable universities.
But if they accept anything, it means that the journal is "omnivorous" and of no value.
All the valuable scientific journals in the world, whether in the field of mathematics or non-mathematics, must properly screen(sieve) the article and not publish "anything in any topic".
Definitely a good feature of a paid journal is that it is specialized, has enough time to judge and, of course, a reasonable cost to publish the article.
For example, Springer Open Journals are of good agreement with mentioned notes.(https://www.springeropen.com/)
Do not believe Any journal their title started by the words : International or Global or universal, they accept every research and the important you pay