At what MRR do you actually pull the trigger on paid ads?

Living in the Google Ads and media buying trenches, I constantly see makers make one of two mistakes: either burning cash on Performance Max campaigns before having true product-market fit, or relying purely on organic hustle for so long that they starve their own growth.

For those of you who have successfully scaled, what was your exact trigger to start buying traffic? Did you wait for a specific revenue milestone, or did you run search campaigns early on just to validate the offer?