Add a product to an existing Order Summary in Salesforce Order Management

Hi everyone,

I’m trying to add a product to an existing Order Summary in Salesforce Order Management using the Add Order Item Summary Flow action, but I keep getting a generic error with no useful detail.

Here’s what I already verified:

• The Order Summary already exists for the order.
• I can see an existing OrderItemSummary on the same order.
• I’m passing:
  • OrderSummaryId
  • OrderDeliveryGroupSummaryId
  • Product2Id
  • PricebookEntryId
  • Quantity
  • UnitPrice
  • TotalLineAmount
  • Reason
  • Type

The values I’m using are valid picklist/API values in my org, and the flow interview shows the payload being built correctly, but the action still fails with:

I also checked that the order is not being blocked by the summary creation process, and I’m working on a test order with existing Order Summary data.

Has anyone successfully used Add Order Item Summary

in Flow? 

Are there any hidden prerequisites, special field requirements, or order status constraints that could cause this generic failure?

Any advice or examples would be really appreciated.

Thanks!