Invalid iops to storage (GB) ratio for engine name aurora-postgresql and storage type aurora

Question

I tried to create aurora PostgreSQL using troposphere.

self.add_resource(
    rds.DBInstance(
        identifier,
        AllocatedStorage="50",
        Engine="aurora-postgresql",
        MasterUsername="myName",
        DBSubnetGroupName=Ref(subnet_group),
        MasterUserPassword="myPassword",
        DBInstanceClass="db.t4g.medium",
        SourceRegion="eu-west-1"

        
    )
)

When I executed this, I'm getting below error.

Invalid iops to storage (GB) ratio for engine name aurora-postgresql and storage type aurora: 0.0000 

Based on the [1] Iops is not required for Amazon Aurora. Then how can I get this issue? Appreciate your responses.

[1] https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_Storage.html#USER_PIOPS