No do not use the discount block on the invoice

create a dummy bank account, create a service item that has that dummy account as the income account, use that item on the invoice, set the qty to negative one, and enter the amount

create a new inventory item for the trade […]

Resolution for 'create a service issue: 'Trade in vehicle how to invoice' available: Yes.

The create a service 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 create a service issue yourself by looking for a resolution described in the article. If it is a complex create a service issue or you are unable to solve the issue, you may contact us by clicking here or by using other create a service support options.

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