Matlab Symbolic Toolbox returns conditions equal to the input function

I want to check where a symbolic function with two symbolic parameters is negative when the parameters are in some particular range. When I use the following code to analyze the function func, the Sol.conditions returns the function itself (with the specified ranges for the parameters). I do not know how to make Matlab solve this inequality rather than returning what I gave as input.

Sol = solve(func<0,x,y,'ReturnConditions', true);

Similarly, when I use the numerical solver, it gives empty output even for 2nd degree polynomials, where there is at least one root in the specified parameter range. As you can guess, my function is very complicated and I really need to find a way to get it solved somehow, but these results are not promising. Any suggestion?

S= vpasolve(func, x,y, 64)