Charles Ellicott Commentary Exodus 40:29

"And he set the altar of burnt-offering at the door of the tabernacle of the tent of meeting, and offered upon it the burnt-offering and the meal-offering; as Jehovah commanded Moses." — Exodus 40:29 (ASV)

He put the altar of burnt offering by the door of the tabernacle. — On the altar of burnt offering, see Exodus 27:1-8; Exodus 38:1–7. Some preposition has been omitted before the word “door.” Our translators suppose an omission of ’ al, “at,” but it is more probable that liphney, which occurs in Exodus 40:6, is the word omitted. The altar was not “at the door,” but “before” or “in front of the door.”

And offered upon it the burnt offering and the meat offering. — Offered upon it, that is, the first evening sacrifice—a lamb for a burnt offering, together with the prescribed meat offering. (See Exodus 29:40.)