aws-cdk: rds.Credentials: cannot generate secret even having lots of characters excluded

What is the problem?

We are getting this error in cloudformation when trying to create a Postgres instance

Reason: The parameter MasterUserPassword is not a valid password. Only printable ASCII characters besides '/', '@', '"', ' ' may be used. (Service: AmazonRDS; Status Code: 400; Error Code: InvalidParameterValue; Request ID: d463b57c-d017-415a-abd6-454db4b08d84)

but we have added all the possible character we could think of in the except. Being quick before cloudformation rolledback the secret, we could see all the secret contained were regular characters.

Reproduction Steps

This is how we generate the credentials

credentials = rds.Credentials.from_generated_secret(
            username=GENERIC_USERNAME,
            secret_name=secret_name,
            # Excluding chars by PSQL url restrictions
            exclude_characters="^ %+~`#$&*()|[]{}:;,-<>?!'/\\\",="
        )

What did you expect to happen?

Create the master password for postgres

What actually happened?

It couldn’t create it

CDK CLI Version

1.125.0

Framework Version

No response

Node.js Version

The one used by codepipeline

OS

The one used by codepipeline

Language

Python

Language Version

No response

Other information

We are having this problem deploying from local and running a codepipeline deploying the cdk.