Ok, I really can't understand the dynamics of this arrangement. Not with the info provided.
So you don't actually build this product or service, you're just a middle man? Why not just have the vendor include the missing piece?
I think crucial details are being lost in the vagaries.
Exactly. So if we want to be pedants, earth or Earth would be fine here. Even if he's in a building, that building is still on the soil. Even if he's flying in an airplane, that airplane is supported by air, which it itself supported by earth. The only way you can't be "on earth" is if you're in space and/or in freefall. And Musk is too much of a coward to climb aboard one of his own rockets.