If the items are placed with you on consignment, they are not inventory items in QB, inventory is what you own to sell in QB

QB does not do consignment sales  since it can not track a payable % for sales nor post it

One  workaround is to

create a non inventory item, […]

Resolution for 'Consignment Inventory issue: 'Discount on Consignment Inventory' available: Yes.

The Consignment Inventory issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the Consignment Inventory issue yourself by looking for a resolution described in the article. If it is a complex Consignment Inventory issue or you are unable to solve the issue, you may contact us by clicking here or by using other Consignment Inventory support options.

For more information about resolving issues related to Consignment Inventory in Quickbooks/QBO or to get support for the issue 'Discount on Consignment Inventory', click the link below: