Create a new receipt of type refund

I am trying to create a refund receipt by calling the endpoint: https://api.7shifts.com/v2/company/{company_id}/receipts but it doesn't accept a negative value in the net_total field.

I haven't found anything for this subject in the documentation of this endpoint, but in the update receipt https://developers.7shifts.com/docs/sales-integration-update-receipt-data, it indicates that the total should be indicated in negative.

How should we create that new receipt?

Thanks,
Joan