VPN: The log shows "payload processing failed" error message
12/20/2019 1269 31487
The Log message Payload processing failed indicates there is a mismatch of proposals during phase 1 or phase 2 negotiation between a site-to-site VPN. If you observe the logs received just before this error message on the responder SonicWall will clearly display the exact problem.
Logs on Responder
Ensure that the proposals are identical on both the VPN policies.
Click VPN, click the configure icon next to the appropriate VPN SA name.
On the Proposals tab, make sure the IKE (phase 1) Proposal and Ipsec (phase 2) proposal is identical to the remote firewall. Make sure the Perfect Forward Secrecy settings match on the local and remote firewall.
NOTE: In a manual key configuration, the incoming SPI for the main site is the outgoing SPI for the remote site and vice versa.