In OPDK, When a ServiceCallout is made using <FormParam>, Apigee should automatically URL encode the parameters without having to do anything. If Apigee doesn't URL encode automatically. Then, we need to check the message-processor.properties file,
conf/http.properties+HTTPClient.urlencode.request.line=false -> This property will not help Apigee to URL encode the request.
(or)
conf/http.properties+HTTPClient.urlencode.request.line=true -> This property will help Apigee to URL encode the request.
So, To handle special characters in <FormParam> parameter in the serviceCallout policy, conf/http.properties+HTTPClient.urlencode.request.line=true, This property will Apigee to URL encode the requests