Trying to use Canon 60D DSLR with Skywatcher 130P. Can't focus image
As you suspected, the problem is probably that, as with most Newtonian telescopes, the image plane is too close to the outside of the tube, so you can't physically get your camera sensor close enough to the image plane.
There may or may not be adapters that will solve this problem for your specific telescope and camera. Barlow lenses help but aren't always enough. Luckily your telescope is collapsible, so you should be able to bring the image plane far enough out by collapsing the telescope a little. Attach your camera to the telescope as before and slowly collapse the telescope. You should see the image gradually come into focus.