failed to get valid proposal

Hi guys,

need help, I check from log and it keep attack and hit below this error with different ip address

aug/12/2020 10:20:08 xxx.xxx.xxx.xxx failed to get valid proposal.
aug/12/2020 10:20:08 xxx.xxx.xxx.xxx failed to pre-process ph1 packet (side: 1, status 1).
aug/12/2020 10:20:08 xxx.xxx.xxx.xxx phase1 negotiation failed.


is any idea to block ?
please help. thanks