Foreach(multiplecall) can't read result from proceeding xform2hdr

Issue:for-each (or multiple call) can't read input of results from proceeding xform2hdr

A brief induction of scenario:

B1iSN creates both GRPO and Delivery when an XML inbound file arrives FILI

1. The first xform2hdr and singlecall: retrieve additional information from order
2. The 2nd xform2hdr: preapre GRPO and put the results under root element <GRPO>
3. for-each singlecall:  Call B1DI B1.8.8.GR
4. the last xform: involve receiver object B1.8.8.DELV

the message stuck in the queue and end up in the for-each atom. I believe there is something wrong in the reading of input from proceeding xform2hdr.

I checked the output message in debug mode, the input of results from 2nd xform2hd is generatedsuccessfully and which under "b1im:B1IMessage/b1im:Header/Z/GRPO/", I have no idea why it is "Z" not b1im:Z here.

However, seems the for-each can't read the result, I tried several xpath to read the result, all failed.

here below are the output message I got in debug mode.