How to parameterize the secret id in dynamic reference (via resolve keyword) to fetch the secret key in aws cloudformation?

I have stored the RDS password, username and jdbcurl in the aws secret manager and want to fetch the password,etc from aws secret in the cloudformation json template file, and I expect that the secret-id should resolve at runtime based on stackprefix.

I tried fetching it using dynamic reference. It works when I fetch it using

"{{resolve:secretsmanager:dev-myRDSSecret:SecretString:JdbcURL}}"

But I want to parameterize the secret-id on the basis of stack prefix, So I used

"Fn::Sub": "{{resolve:secretsmanager:${StackPrefix}-myRDSSecret:SecretString:JdbcURL}}"

. But this gives me error while deploying -

FAILED: ERROR: Could not create stack summary - An error occurred (ValidationError) when calling the GetTemplateSummary operation: Template Error: Encountered unsupported function: Fn:Sub Supported functions are: [Fn::Base64, Fn::GetAtt, Fn::GetAZs, Fn::ImportValue, Fn::Join, Fn::Split, Fn::FindInMap, Fn::Select, Ref, Fn::Equals, Fn::If, Fn::Not, Condition, Fn::And, Fn::Or, Fn::Contains, Fn::EachMemberEquals, Fn::EachMemberIn, Fn::ValueOf, Fn::ValueOfAll, Fn::RefAll, Fn::Sub, Fn::Cidr]

Can someone here suggest how we can parameterize the secret-id here?

You can use the !Join function to assemble the secret string reference, assembling the pieces one by one:

{
  "Fn::Join": [
    "", [
      "{{resolve:secretsmanager:",
      {
        "Sub": "${StackPrefix}"
      },
      "myRDSSecret:SecretString:JdbcURL}}"
    ]
  ]
}

I suspect a sub on the whole string errors because of the {{ brackets (which you need anyway) interfering with the interpolation syntax.