I am working in Professional edition where I need to prevent the creation of a Lead if there is an Opportunity present with the same Unit_Id.
I created a Process Builder, a flow and a validation rule on Lead. The flow performs a lookup on Opportunity on Unit_Id. If a matching Opportunity is found, it set a Boolean field on Lead (Is_Duplicate) to True. The validation Rule is using this field to detect if it's duplicate or not .
When I create/edit a Lead with a duplicate Unit_Id, I get the below error. Surprising part is when I turn the validation rule off, I get no error. As soon as I turn it on, it is happening. This tells me that Process and Flow are working correctly from data update perspective at least
We can't save this record because the “Prevent Duplicate Lead” process failed. Give your Salesforce admin these details. An unhandled fault has occurred in this flow
An unhandled fault has occurred while processing the flow. Please contact your system administrator for more information. Error ID: 556950787-34611 (-482689395)