Acknowledgments are not receiving from XI to R/3

Hi Experts,

We sent some IDOCS to frontend system called XXX via XI.We should receive the Inbound ALExxx IDOCS as acknowledgments, but they are not coming into R/3.

(Note: FYI.in R/3 we used get the acknowledgment for each of the outbound WP_PLU IDOC sent to XI.)

when we observed in XI we could see that the acknowledgments are hold status. i checked in runtime work bench to get error logs but i couldn't see any error messsages in message monitoring.could someone help on this ?what could be the reason for this?

Aprreciate for your help

Thx,

Amar