Please remember that when you accept a delivery on the app, you are answering a client's urgent need. You have committed to providing your service for this delivery.
On slot, cancelling a delivery you accepted is only possible when:
The weight of the package exceeds the limit for your transport type (see limits here)
The pick-up distance is above the limits for your transport type (see limits here)
The package is too large to fit your transport type and be delivered safely
You have had an accident
Your vehicle has broken down and you are unable to complete the delivery successfully
When this happens:
Explain in your first sentence the reason for the cancellation request
Send proof of the issue - photos
If the reason is not valid you will be ineligible for Minimum Guarantee for this slot and you will receive "unauthorised courier request" invalidation message the next day.