Faris,
Once you route EDI 850 to TradingNetowrks,the processingRule will be triggerg depends on the SenderID/Receiver/DocumentType and this rule will process to a flowservice this service input should be bizdoc(wm.tn.rec:BizDocEnvelope)this will be in the pipeline along with editn_ts,edidata.So extract the X12 850 content from either of these variables or use bizdoc/Content(bytes) and invoke a service bytesToString output is 850 string.
For debugging as a first step invoke savePipelineToFile and later restorePipelineToFile and make sure that bizdoc,editn variables exists in the pipeline.
Please use the search functionality in this site,since lot of times this basic procedure has been discussed,this saves your time too…
HTH,
RMG.
#edi#Integration-Server-and-ESB#webMethods