i think you're supposed to use the polygon command with index above 0 (0 is a special delete all case).
this creates a line for me
// Project: spriteshapepoloygon
// Created: 2018-08-08
// show all errors
SetErrorMode(2)
// set window properties
SetWindowTitle( "spriteshapepoloygon" )
SetWindowSize( 1024, 768, 0 )
SetWindowAllowResize( 1 ) // allow the user to resize the window
// set display properties
SetVirtualResolution( 1024, 768 ) // doesn't have to match the window
SetOrientationAllowed( 1, 1, 1, 1 ) // allow both portrait and landscape on mobile devices
SetSyncRate( 30, 0 ) // 30fps instead of 60 to save battery
SetScissor( 0,0,0,0 ) // use the maximum available screen space, no black borders
UseNewDefaultFonts( 1 ) // since version 2.0.22 we can use nicer default fonts
setPhysicsScale(0.2)
setPhysicsGravity(0,0)
SetPhysicsDebugOn()
s = CreateSprite(0)
SetSpriteSize(s,200,200)
SetSpritePositionByOffset(s, 200, 200)
SetSpriteShapePolygon(s, 3, 1, -100.0, -100.0)
SetSpriteShapePolygon(s, 3, 2, 100, 100)
SetSpriteVisible(s, 1)
SetSpritePhysicsOn(s, 1)
do
if GetRawKeyReleased(27) then end
Print( ScreenFPS() )
Sync()
loop
life's one big game
spec= 4ghz, 16gb ram, AMD R9 2700 gpu