Miles Booster on reward flight?

I booked a reward flight using miles. The system seems to let me pay for Miles Booster for this flight. Is that right, or will they cancel the order?

Thanks!

Clause 8 of the Miles Booster T&Cs clearly states that it is allowable.

8. Miles can be purchased through Miles Booster with flights that were purchased or upgraded via the redemption of Flying Club Miles.

|:)

It might be an idea to double check that the miles actually do post and stay in your account after taking the flight though... VS IT can be a tad unreliable at times.