Django85 nice catch.
How should it be calculated?
Currently if you have set it based on % of delivery charge, and if the delivery charge is 0, then the earnings will become 0 as well (which is obviously not ideal)
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Edit:
If we save the actual delivery charge also, and use this to calculate the delivery commission, then this issue can be solved. (This delivery charge will not be shown anywhere, it will only be used to internally calculate the delivery guy commission)