I am having hard time in learning constraints & auto-layout in iOS.I have used any-widt
The Add Missing Constraints
error is shown because you have not provided vertical constraints, may be height constraints or vertical position constraints.
To fix this use the blue dotted guide lines to place your view and then click on "Reset to suggested Constraints" or you can provide the vertical constraints according to your requirement.
Xcode maybe warning you for button width because by default the text label of button takes the default padding space.
To add custom padding you should change the insets
of your button contents from the storyboard.
maybe post a picture of what your layouts look like in the story board so we can understand your problem better, but also as a rule of thumb, make sure you have constraints that will satisfy an x and y position, and a width and height, if all those are satisfied your layout wont be ambiguous. from what you have said, it sounds like you only satisfy 3 of those criteria, leaving y position out (maybe add center vertically or top space).
it may be asking you to reduce the width and height of your constraints because the value of the constraints is less than what they are in the visual representation on the storyboard, just click on the constraints and see what their value is.
ok check out the image and constraints here...
you need to give width and height constraints too....also need to give x and y position of button. so that screen knows the alignment from where to start drawing the button with how much width and height