Form validation last validation

As far as I know the callback can only be called on a direct field, not on fields grouped together, or am I wrong there?

I am now doing a callback on every field to check if the value is more than 500.00, but it returns multiple errors on every field then when the value is higher than 500.00, that's the problem I am struggling with.

So I'm not sure if there's a way to do it using a callback to check if all fields grouped together > 500.00.