I am trying to get place a ushort into an ArraySegment<byte>, but I am unable to get the 2nd byte of the ushort due to this exception.

public unsafe static void SetUshort(in ushort value, in int i1, in int i2, in ArraySegment<byte> arr)
{
     var b = (byte)((value >> 8) & 255);
     arr[i1] = b;
     arr[i2] = (byte)value;
     //fixed (byte* p = arr.Array)
     //{
     //    var ptr = p + arr.Offset;
     //    Buffer.MemoryCopy(&value, ptr, 2, 2);
     //}
}
public static ushort GetUshort(int i1, int i2, ArraySegment<byte> arr)
{
    return (ushort)(arr[i1] << 8 | arr[i2]);
}

    [Test]
    [TestCase(ushort.MinValue, 0, 1)]
    [TestCase((ushort)5614, 0, 1)]
    [TestCase(ushort.MaxValue, 0, 1)]
    public void SetUshort_Correct(ushort testValue, int index1, int index2)
    {
        Helper.SetUshort(testValue, index1, index2, Body);
        Assert.That(Helper.GetUshort(index1, index2, Body), Is.EqualTo(testValue));
    }

I’ve tried to use pointers, which works.