2022
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Let us take an example of custom field SalesRep__c on Opportunity in Salesforce.
We have to map this field to SalesRep custom field in QuickBooks online. This is created in sales section as shown in the following screen shot:
To map this field, choose any one of the fields that is not used for mapping any values. Then, type custom field name (SalesRep) in the target area i.e between <Name> </Name> tags (QuickBook Online) and add the following query in the source field.
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<StringValue>"+VALUE("SalesRep__c")+"</StringValue>: The custom field in Salesforce.