Getting Unable to cast object of type 'System.Guid' to type 'System.String MESSAGE for SearchProcessedOrdersPage API


I am getting the below response to API call


with following parameters



Orders from Linnworks response:{"Code":"-","Message":"Unable to load orders: Unable to cast object of type 'System.Guid' to type 'System.String'."}

Can I anyone shed some light into this and how to rectify this issue

1 person has this problem

Hello Kevin,

We have checked and tested the method and can confirm that there might be an issue with it.

Currently, we cannot provide ETA on its resolution, however, you have two options in order to get that information:

  1. In the Processed Orders tab, right-click on the column title and disable the "Fulfilment Location".
  2. Use the SearchProcessedOrder method which is very similar to the one that you are already using. You can find more information about the endpoint here:

Kind Regards,



We have the same issue, option #1 doesn't work in our case.

To implement option #2 we need to spend some time on our side, and we hope this will not be in vain. Could you please clarify:

  • When do you plan to fix this issue? 
  • What is the difference between these two methods and is there any guarantee that the new method will not have this problem?


Hello Elena,

The fix for the issue is already in verification, however, unfortunately, I am not able to advise when exactly it will be deployed.

Can you please double check the first suggestion? I can see that the "Fulfilment Location" column is still enabled in the Processed Orders screen.

I would also advise you to raise a Support Ticket in the '' Category - 'API' Sub-category providing the full call you are making and the response containing error, so our API team can look further into it and find an appropriate solution for your case if the suggested one does not work. It will also be possible to link the ticket to the development card internally and you will get notified once the fix is released.

Kind Regards,


Hello Marina,

Thanks for the reply. We checked the first option with “Fulfilment Location”, but it did not work, so we moved the field back to the table of processed orders.

Option number 2 (a new method) solved the problem with processed orders. Now we just hope that after the fix you make, this method will continue to work correctly :)



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