It doesn’t need to be directly reciprocal. You could have a system where having your paper peer reviewed costs X tokens, and you earn tokens by peer reviewing other papers that don’t have citation links to yours. Or you buy tokens with cash which sustains a fund for external reviewers. Or other people can transfer their tokens to you.

Would that still have problems?

Sure, but the identical exchange of value occurs in the current system, it just goes unsaid/unspoken. You review my journal and maybe ignore some of the problems, poor assumptions, whatever crap I used to make the sausage, just let me get it published; I do the same for you. You may not 'know' who is reviewing your journal, but at least in the natural sciences, there are so few technically qualified individuals to review some very domain specific publications, so its almost inevitable that although you may not know for sure who is reviewing your paper, you can figure it out without too much work. Since both reviewers and authors benefit from getting their own work published, there is a silent consensus for letting bad work slip through.

No obviously I don't mean you review a person's paper and they review yours - use your common sense, mate.

I mean if you publish a paper and get four reviews, you then review another four papers at some point - perhaps at an entirely different conference later that year. You just make sure you review at least 4n papers for each n papers you publish.