At once and on the spot and At once

At once and at once and on the spot are semantically related. In some cases you can replace phrase "At once" with "At once and on the spot", this phrases are similar.

At once adverb - Without delay or hesitation; with no time intervening.

At once and on the spot and at once are semantically related. Sometimes you can replace phrase "At once and on the spot" with "At once", this phrases are similar.