Unable to see Payload in SAP PI7.31 Single stack

Hello Experts,

We have a scenario of Mail as sender and ECC as reciever using Proxy. We are using SAP PI7.31 single stack.

Here we are reading the file from mail attachment which is in CSV format and sending the data to ECC successfully.

But while to check the payload in Message Monitor, while click on the "Mailattachement-1.csv" it is opening with "No Message Selected".

Can someone please let me know how can I check the payload of the attachement.

Thanks

VR