Getting error while using Kerberos authentication

i ve created a rds postgres instance and AWS managed in the same VPC . created the user in AD and RDS. when i try to connect to RDS via Kerberos authentcation from the domin joined EC2, am getting the below error :

psql: error: connection to server at "abc123.us-east-1.rds.amazonaws.com" (172.31.96.61), port 5432 failed: FATAL: GSSAPI authentication failed for user "rdsuser@xyz.com" am able to connect to the rds instance from the domain joined ec2 using password Authentication