AWS EventBridge Rule with Redshift - Procedure not being called

Question

I've created an event rule to call a redshift stored procedure, using temporary credentials.
From Redshift I can see that the role is successfully getting credentials to log onto the cluster & db as the intended user ..but I cannot see any trace of the Stored Procedure being called.

User has Grant Usage on the correct schema, and execute on the procedure itself. Nothing in STL_QUERY or STL_ERROR to even show an attempt at a call.

Looked in CloudTrail, I can see an 'ExecuteStatment' event with 'Success', but the requestparameters.sql value is given as "OMITTED".

Unsure where to look next in order to find the issue ? I'm assuming that once the connection has been authenticated, then nothing AWS IAM related would be involved further.

Wondering if I've missed something obvious, or a quirk of eventbridge conifg/functionalty ?

Event Rule target

{
        "Targets": [
            {
                "Id": "target_xxxxxxxxx",
                "Arn": "arn:aws:redshift:us-east-1:xxxxxxxxxxxx:cluster:xxxxxxxxxx",
                "RoleArn": "arn:aws:iam::xxxxxxxxxxx:role/xxxxxxxxx",
                "RedshiftDataParameters": {
                    "Database": "xxxxxxxx",
                    "DbUser": "service_xxxxxxxxxx_scheduler",
                    "Sql": "CALL control.post_load_refresh();",
                    "StatementName": "myteststatement",
                    "WithEvent": false
                }
            }
        ]
    }

STL_CONNECTION_LOG

username: IAM:service_xxxxxxxxxx_scheduler
event: authenticated
event: initiating session
event: set application_name
event: set application_name event: disconnecting session

DB Perms to execute procedure

GRANT USAGE ON SCHEMA control to "IAM:service_xxxxxxxxxx_scheduler";
GRANT EXECUTE on PROCEDURE control.post_load_refresh() TO "IAM:service_xxxxxxxxxx_scheduler";