522 FTP Reply Code - KB Article #1980Related Articles --
522 Network protocol not supported, use (1,2).
A 522 reply code may be sent in response to an EPRT/EPSV command which uses the incorrect AF. Valid AFs are 1 for IPv4 and 2 for IPv6. It is a transient negative reply, which means the client is encouraged to reissue the command with a valid network protocol identifier.
A 522 reply code may be sent in response to the EPRT or EPSV commands.