Insets isn't the way to go. You use inset for padding a view's internal content from its margins. For what you need your best option is to wrap your vwGroup inside another UIView and set the border in the wrapping view. Something like:

let wrappingView = UIView(frame: someFrame)
wrappingView.backgroundColor = .clear
wrappingView.layer.borderColor = UIColor.yellow.cgColor
wrappingView.layer.borderWidth = 2.0;
wrappingView.addSubview(vwGroup)

Of course this is just for you to get the big picture. You might want to set proper frames/constraints.

swift 5.4

call like this:

customView.layer.innerBorder()

did it, by add a sublayer

extension CALayer {


    func innerBorder(borderOffset: CGFloat = 24.0, borderColor: UIColor = UIColor.blue, borderWidth: CGFloat = 2) {
        let innerBorder = CALayer()
        innerBorder.frame = CGRect(x: borderOffset, y: borderOffset, width: frame.size.width - 2 * borderOffset, height: frame.size.height - 2 * borderOffset)
        innerBorder.borderColor = borderColor.cgColor
        innerBorder.borderWidth = borderWidth
        innerBorder.name = "innerBorder"
        insertSublayer(innerBorder, at: 0)
    }
}

Try this, it is helpful for you.

First, Add this extension

extension CALayer {
    func addGradientBorder(colors:[UIColor],width:CGFloat = 1) {
        let gradientLayer = CAGradientLayer()
        gradientLayer.frame =  CGRect(origin: CGPoint.zero, size: self.bounds.size)
        gradientLayer.startPoint = CGPoint(x:0.0, y:0.0)
        gradientLayer.endPoint = CGPoint(x:1.0,y:1.0)
        gradientLayer.colors = colors.map({$0.cgColor})

        let shapeLayer = CAShapeLayer()
        shapeLayer.lineWidth = width
        shapeLayer.path = UIBezierPath(rect: self.bounds).cgPath
        shapeLayer.fillColor = nil
        shapeLayer.strokeColor = UIColor.red.cgColor
        gradientLayer.mask = shapeLayer

        self.addSublayer(gradientLayer)
    }
}

Then add the UIView with border

let vwGroup = UIView(frame: CGRect(x: 50, y: 150, width: 200, height: 200))
vwGroup.backgroundColor = .red

//-- This is for padding between boarder and view -- you can set padding color ---
vwGroup.layer.addGradientBorder(colors:[UIColor.black,UIColor.black] , width: 40)

//--  This is for outer boarder -- you can also change the color of outer boarder --
vwGroup.layer.addGradientBorder(colors:[UIColor.white,UIColor.white] , width: 10)
self.view.addSubview(vwGroup)

Output is: