How to filter results of one SDP from another

Summary

How to filter results of one SDP from another

Content

I have a an application that is using an Oracle Fusion Applications ERP REST endpoint to retrieve a list of suppliers configured as an SDP providing data to a combo-box and need to provide a list of supplier sites to another combo-box using another REST SDP using the following endpoint by passing in the supplier ID returned from the first one:

/fscmRestApi/resources/11.13.18.05/suppliers/{SupplierId}/child/sites

The response type from the first SDP is configured to return supplierId, supplerName, and supplierNumber, but I cannot determine how to access the SupplierId.  I've tried creating a ComboboxOneValueChangeChain to assign the value to a variable to assign data to the parameter for the sites SDP  and also tried to set the SDP parameter directly but don't see any of the fields listed in the variable mapper  (see attached screenshot).