There is 2 reasons why you might see this error

1-Your vendor Flex client is a newer version that your server
2-Your license opt file checksum failed because it was created for a newer rlm

If its the first just upgrade your rlm server to match your client version, or above

For the second upgrade your rlm server to match your opt client vendor version
Opt files are backwards compatible, existing lic files will not need to be updated from your vendor