My Field Map tries to transport a webservice ID

[joebordes]

the correct syntax to get the record ID is:

$(assets_related_soid : (SalesOrder) record_id)

https://github.com/tsolucio/coreBOSTests/blob/master/modules/com_vtiger_workflow/expression_engine/VTExpressionEvaluaterTest.php#L574

try that and confirm