hello, how to write this system?

> restart;
> x10:=0.2; x20:=0.4; U0:=0.25;
> eq3 :=subs(U(t)=(piecewise(U(t)<=0,0,U(t)>=1,1,U(t))),(1/4)*(U(t)^2*x1(t)-2*U(t)*x1(t)*sqrt(x2(t))-U(t)^2*x2(t)+2*U(t)*x2(t)*sqrt(x1(t))-2*(diff(U(t), t))*x1(t)^(3/2)*U(t)+4*(diff(U(t), t))*x1(t)^(3/2)*sqrt(x2(t))+2*(diff(U(t), t))*x2(t)^(3/2)*U(t)-4*(diff(U(t), t))*x2(t)^(3/2)*sqrt(x1(t)))/(x1(t)^(3/2)*x2(t)^(3/2)));
> sys := eq3=0, diff(x1(t), t) = (piecewise(U(t)<=0,0,U(t)>=1,1,U(t)))-sqrt(x1(t)), diff(x2(t), t) = (piecewise(U(t)<=0,0,U(t)>=1,1,U(t)))-sqrt(x2(t));
> dsolve({sys,x1(0)=x10,x2(0)=x20,U(0)=U0},{x1(t),x2(t),U(t)},type=numeric);

Male produces an error: Error, (in DEtools/convertsys) invalid input: eval expects its 2nd argument, eqns, to be of type {integer, equation, set(equation)}, but received newdeqns