Why does the following not compute?

MaxValue[-y^2, y \[Element] Interval[{-1, 1}]]

I expect it to compute the maximum value of the funtion over the interval from -1 to 1 but I instead get the error: MaxValue::objfs: The objective function {-Subscript[y, 1]^2} should be scalar-valued. What should I be using instead?

Why does the following not compute?

MaxValue[-y^2, y ∈ Interval[{-1, 1}]]

I expect it to compute the maximum value of the funtion over the interval from -1 to 1 but I instead get the error:

MaxValue::objfs: The objective function {-Subscript[y, 1]^2} should be scalar-valued.

What should I be using instead?