What does the Service due / maintenance reminder mean?

The car has reached its scheduled service interval by mileage or time.

How much does it cost to fix the Service due / maintenance reminder?

Typically $60 to $400 in the US, depending on the cause. An oil change at the low end; a major interval service at the high end.

Urgency:Service soon

Yes. It is a reminder, not a fault — but skipping the service shortens the life of the engine and voids some warranties.

$60 – $400

An oil change at the low end; a major interval service at the high end.

A typical range, not a quote. Actual cost depends on the car, the shop and the fault.