HI
I use SOA 12c with all components 12.2.1.3.0 version.
I can make REST proxy service with template parameters but I am unlucky to create REST proxy service with query parameters.
I create this service the same way as proxy service with template but at the end I choose query for parameter.
At the start I create Business component for https://restcountries.eu/rest/v2/alpha?codes=sk as reference with base URI https://restcountries.eu/ and resource path /rest/v2/alpha, and GetCountry method on this resource with HTTP verg GET and parameter "codes" query style and type string. This creates WADL resource.
Then I create REST type pipeline based on the same WADL resource as business reference and let expose pipeline as proxy service (transport http). Slightly change endpoint URI and test.
I got
<Nov 15, 2018 11:12:29,333 AM CET> <Error> <oracle.osb.pipeline.kernel.router> <OSB-382191> <CountryQueryProxy/Pipeline: Unhandled error caught by system-level error handler: com.bea.wli.sb.pipeline.PipelineException: Transport error (error code=OSB-380000): null