Need help with a constraint using the operator is within

When I put in operator is within, the maximum distance shows up with a RED add box, I just want to type in a number but it doesn’t let me put anything in or even select the next box to use miles, am I doing something wrong?

In most setups, “is within” needs a reference point before distance unlocks. If the location or object field is empty or invalid, the distance input stays disabled and flags red. Try setting the base location first, then the unit selector and number should become editable. Sometimes a refresh helps if it bugs out.