By default, the SYS user is used for redo transport in Data Guard configurations. Data Guard communication uses password files in the standby databases to authenticate redo transport sessions. If we change the password of the SYS user in the primary database, redo transport sessions will not be authenticated because the password file in the standby site will be outdated. So redo transport will raise the ORA-01017: invalid username/password or ORA-01031: insufficient privileges error. The primary database alert logfile will include the following lines:

Error 1017 received logging on to the standby
PING[ARC0]: Heartbeat failed to connect to standby 'INDIAPS'. Error is 16191.

It can also include the following lines:

ORA-01031: insufficient privileges
PING[ARC2]: Heartbeat failed to connect to standby 'INDIAPS'. Error is 1031.