Key is empty when passing to external association service

Dear Expert,

I have problem with passing the key to external association service.

For example,

I have 2 service and create external association and navigation properties by following this guide Fiori Extension - Reuse OData/UI components - Part 1

i have successfully linked services as picture below.

and no error in target service.

When I debug abap code in target system. The parameter it_key_tab should pass key (SalesOrganization , Distribution Channel , Division , ProductID , CustomerNo) from source service but it's always empty. Have I missed something?

Thank you.