2022
...
TargetField > VALUE("CustomField[Name='Custom_Field name']/StringValue").
Let us take an example of custom field SalesRep in Invoice of QuickBooks Online. To retrieve the value of this field and to insert in the Target field Salesrep__c of Salesforce OpporunityOpportunity.
TargetField should be Salesrep__c.
The query to retrieve the value from custom field SalesRep should be:
VALUE("CustomField[Name='SalesRep']/StringValue")