Is it a lawful order if it is given over a text message/social media? Where can I find the reference?

There is no way a lawful order cannot be delivered. One might be able to show it was not delivery to them with the method used but now I think every soldier carries a phone that is used for official business all the time. So I would say that yes an official order may be given over phone. Way back when the dinosaurs were roaming I personally called people on the land line and told them things like there is an alert get back to the company. And thousands of orders are delivered by radio. So if you get it you obey it. No matter how you got it. And if I was serving now and you challenged receiving order by phone. My solution to that problem would be to put you in quarters on post in the company area

I !UST certainly admit, though I obv haven't a clue as to the answer, that is certainly an interesting question, by all means....