Ich habe eine Wette auf das Team abgeschlossen.

English Translation

I made a bet on the team.

“Auf” when not denoting movement should be dative case, therefore “auf dem Team” sounds more correct. Where is this statement wrong?

The dative case usually tells where you (the actor) are while the action happens, but in this case the movement is about the object (“Wette”) and where it goes (“auf das Team”).
Think putting chips onto a square of a roulette table.

“auf dem Team” would sound funny because how would one be on top of a team and make a bet while being there…

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