M class is used for both basic and standard fares. From what I've seen so far, AS can't sell PD basic fares because all of them have language that it needs to be ticketed by PD.

You can confirm whether you have a basic fare by looking at the fare rules under the Changes section. If it shows a fee to change, then it's standard. If it states no changes, then it's basic.

Another way to check is through My Bookings on the PD website. There's a section labelled Fare Rules which should show what type of fare you have on the PD side.

Also keep in mind that M class is not listed as an eligible fare class for mileage earning, so not clear if a Standard/Main M class fare will earn miles.