suru verb (special)
make a done deal; finalize; seal the deal
Colloquial business/negotiation term derived from English 'done'. Used when an agreement is confirmed or a deal is closed.
先方と話して、この条件でダンしよう。
Let's talk with the other party and seal the deal on these terms.
契約はもうダンしたから、あとは書類
The contract is already a done deal, so all that's left is to exchange the documents.