You can't mix free processing with paid processing when the promotional point balance is zero. If you have 300 promo points and 300 paid points and try to do a job that requires 400 points it will take the 300 promo points and 100 paid points.
If 70 images takes 249 points and would be free you need to have enough paid points to process 71 images that would be 254 points.
In step 2 of the DJI specific workflow you can check a box that forces paid points ('Force Paid') to be used in place of free points.