Getting dragon fruit seeds started is easy, but they'll need sustaining thereafter. Your dragonfruit seeds need some nutrients to sprout to become healthy dragonfruit seedlings as well as water, as once the dragonfruit seeds have sprouted and begin to put down their first roots they will begin at once to rely upon nutrients outside of those in the dragonfruit seed itself.
A good source of these nutrients for the growing dragonfruit seeds can be found in any high quality potting soil, but because you are looking for a very loose soil medium for growing dragonfruit seeds to dragonfruit seedlings, you do not want to use this 'soil' alone. You want to add at least an equal portion of a loose filler like perlite or tezontle (a light and porous volcanic rock) to the potting soil to give your final base mix in which you will sow the dragonfruit seeds. The exact mix is not critical, but you should use at least 50% of the perlite or tezontle if not more.
Note: Whether you use tezontle or perlite as the soil additive, make sure you sift out any accumulated dust before you mix the perlite or tezontle with the base soil. Depending upon the shipping conditions, you may find a lot of fine dust in either of those additives. You want to make the soil looser - not denser!
Next -> Sowing the Dragonfruit Seeds