Is there a way to extract a payload(body day) as a reference for load balancing?

can you try backslash before double quote?

by the way, i do not think period (.) is in payload. 0x20 is space (not period).

e.g.

 configuration

root@(ve11a)(cfg-sync In Sync)(Active)(/Common)(tmos) list ltm virtual bar
ltm virtual bar {
    destination 172.28.20.15:80
    ip-protocol tcp
    mask 255.255.255.255
    profiles {
        http { }
        tcp { }
    }
    rules {
        myrule
    }
    source 0.0.0.0/0
    source-address-translation {
        type automap
    }
    vs-index 29
}
root@(ve11a)(cfg-sync In Sync)(Active)(/Common)(tmos) list ltm rule myrule
ltm rule myrule {
when HTTP_REQUEST {
  if { [HTTP::method] equals "POST" } {
    if {[HTTP::header exists "Content-Length"] && [HTTP::header "Content-Length"] <= 1048576} {
      set content_length [HTTP::header "Content-Length"]
    } else {
      set content_length 1048576
    }
    HTTP::collect $content_length
  }
}
when HTTP_REQUEST_DATA {
  log local0. "payload [HTTP::payload]"
  if  { [HTTP::payload] contains "profileId=\"825\"" } {
    pool A_pool
  } else {
    pool B_pool
  }
}
when HTTP_RESPONSE {
  log local0. "cs [IP::client_addr]:[TCP::client_port] > [clientside {IP::local_addr}]:[clientside {TCP::local_port}] ss [IP::local_addr]:[TCP::local_port] > [IP::remote_addr]:[TCP::remote_port] pool [LB::server pool]"
}
}
root@(ve11a)(cfg-sync In Sync)(Active)(/Common)(tmos) list ltm pool A_pool
ltm pool A_pool {
    members {
        200.200.200.101:80 {
            address 200.200.200.101
        }
    }
}
root@(ve11a)(cfg-sync In Sync)(Active)(/Common)(tmos) list ltm pool B_pool
ltm pool B_pool {
    members {
        200.200.200.111:80 {
            address 200.200.200.111
        }
    }
}

 testing

[root@ve11a:Active:In Sync] config  tail -f /var/log/ltm
Dec 25 23:39:26 ve11a info tmm[2836]: Rule /Common/myrule : payload country="us"profileId="825"localization="GMT+0"
Dec 25 23:39:26 ve11a info tmm[2836]: Rule /Common/myrule : cs 172.28.20.20:47120 > 172.28.20.15:80 ss 200.200.200.14:47120 > 200.200.200.101:80 pool /Common/A_pool

Dec 25 23:39:34 ve11a info tmm1[2836]: Rule /Common/myrule : payload country="us"profileId="999"localization="GMT+0"
Dec 25 23:39:34 ve11a info tmm1[2836]: Rule /Common/myrule : cs 172.28.20.20:47121 > 172.28.20.15:80 ss 200.200.200.14:47121 > 200.200.200.111:80 pool /Common/B_pool