AS2 sender adapter 403 forbidden error

Hi Experts,

I have a scenario which is connecting with third party using sender AS2 adapter.

while third party sending message to PI they are getting 403 forbidden error.

sender agreements are created one for MDN reports and another particular interface for the same sender party and receiver party.

certificates are installed properly and message subjects & AS2 ID also maintained correctly.

i am using pi7.11 version and seeburger AS2 adapter.

Please suggest any configuration or setting if missed which causes this issue.

Thanks in advance.