The 404 Not found indicates that the record that you are trying to reach cannot be found. This can occur if you are passing an incorrect ID. For example, using the Salesforce ID to retrieve a NetSuite record.
Example of 404 Not found
Solution
Verify that the datapills are mapped to the correct fields.
Check that the record ID is valid for the applications (i.e. use a Salesforce_ID for a Salesforce record).
Check that the record ID is valid for the object types (i.e. use a Customer_ID for a customer object).
Check that the record has not been deleted.