Misleading error message for not adding =? for the function labeled argument

[DZakh]

The error says:

This function should have type
  (
~estimatedRetailPrice: Money.t=?,
~mileage: Vehicle.Mileage.t,
) => (~onSuccess: unit => unit, ~onFailure: string => unit) => unit
but its first argument is labelled ~estimatedRetailPrice

But what it actually wants is for me to add =? after ~estimatedRetailPrice as _.

[zth]

Let me know if you're interested in taking a stab at it, we could throw some ideas around on how to make it better and where the actual code is located?