I had a "no sd card" message and thought that there was a problem with my Mavic Pro. As with one other user, I found that my iPad mini was not plugged into my controller. Plugging it in solved the issue.
My ipad was powered up and DJI go opened, i just wasn't cabled into the controller.Can I ask where you saw this message? If your iPad mini wasn't plugged in, where did the message appear?