The Louth side face BATE Borisov in the next round
Dundalk won their first European Cup tie since 1979 on Wednesday night.
The back-to-back Premier Division champions drew 2-2 with Icelandic champions FH Hafnarfjordur to advance to the next round via the away-goals rule.
Dundalk's win means they now meet BATE Borisov in the third qualifying round. No matter what happens against the Belorussian champions, the Louth side are guaranteed at least one other tie, in either the Champions League or Europa League.
The result in Iceland guarantees Stephen Kenny's side a massive payday. Compared to earning €110,000 for potentially winning the Premier Division this year, Dundalk have guaranteed at least €1million by advancing to the BATE Borisov tie.
Earning €300,000 for playing in the second qualifying round, Dundalk will pocket another €400,000 for the next round. Assuming they lose to the Champions League group stage regulars, Stephen Kenny's side would move to the Europa League play-off round where another €230,000 would be pocketed.
If Dundalk were knocked out at that stage, they would also pocket €250,000 for failing to reach the Champions League group stages as national champions.
Those numbers mentioned are only from the UEFA prize-pool fund, and do not include potential match-day revenue or television rights. Dave McMillan's two goals could be the two most valuable in the club's recent history.