Bills for the Hochul-Mamdani pied-à-terre tax haven’t even gone out, yet the Rube Goldberg scheme is already collapsing.

It’s now certain that fewer than 9,000 homeowners will have to pay it, though Gov. Kathy Hochul and Mayor Zohran Mamdani counted on 13,000 to pony up, raising $500 million for the city’s budget.

Yet City Hall has already approved appeals for nearly 7,000 of the 17,000 homeowners it told might be liable, with another 3,800 more yet to be processed.

That’ll mean less — possibly far less — revenue than anticipated (just as city Comptroller Mark Levine predicted).

“Once primary residences are removed and overstated market values are challenged, we may find that the amount actually collectible is significantly less than projected,” warns a lawyer for plaintiffs challenging the tax, Ben Williams.

And that assumes the courts even let the tax stand: Homeowners have filed three lawsuits, including two that claim the tax is unconstitutional and one contesting a key requirement.

This thing was a kludge from the start.

Mamdani needed to convince his socialist base he was slapping the rich, as promised; that’s why he gloated on video about how he was hitting them with this levy, singling out Citadel CEO Ken Griffin (who responded by expanding his company in Florida instead of New York).

Eager to please the mayor and his base, the ever-spineless Hochul blithely broke her no-new-taxes vow, then had her minions design the levy to deliver the city half a billion a year.

Except it’s now clear they had no idea what they were doing . . . if Hochul or Mamdani even cared.

Ironically, soaring Wall Street profits will likely generate enough unanticipated tax revenue to offset all the lost pied-à-terre cash.

That is, the mayor will be bailed out by the success of the very fat cats he demonizes — meaning he’s lucky his policies didn’t work.