Hello,
Here is a more official answer from PM that owns this part of the product:
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Yes, by design and here’s a reason why this is not out of the box.
Salesorderid is GUID in Sales length 36, which means it can’t be used in our Code20 field.
We also can’t safely use ordernumber as it’s autonumber in sales, which might be set by users to something again larger than would fit Code20 which is part out sales order primary key in BC.
Due to above, we leave it to partners and customers to define and synch as needed.
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Thanks.