Below you find the required configuration for the target project to be able to process the parameterized call from the source project (QueryCenter project).
The HTTP call will look like this:
externalcall.jsp?project=bregenz_combined_views&query=grundstuecke&keyname=KG_GNR

Query configuration of target project: External Layer ID 'grundstuecke'

Search field configuration of target project: Search field KG_GNR