How to debug "Transform AWS::Include failed with: The location parameter is not a valid S3 uri."

Question

I have a CloudFormation template (YAML) that includes the following:

```
        Fn::Transform:
          Name: AWS::Include
          Parameters:
            Location:
              Fn::Sub: s3://${TemplatePath}/${SnippetFile}
```
Although I have verified the validity and accessibility of the S3 path with the expected values of these variables, the output fails with "Transform AWS::Include failed with: The location parameter is not a valid S3 uri." There is nothing to indicate the path it _tried_ to use, so I'm not sure how to debug. There appears to be nothing useful in either the console or the output.

Questions:

1. Have I done something obviously wrong syntactically? (I don't normally use the long-form functions but need them here for reasons not relevant to the question)
2. How do I debug in the absence of more detailed error messages?

Answer

Hello Ed,

The error "Transform AWS::Include failed with: The location parameter is not a valid S3 uri" occurs when the S3 URI that CloudFormation expects is in an incorrect format. CloudFormation expects a valid S3 URI such as s3://MyAmazonS3BucketName/MyFileName.json.

Note that using long hand 'Fn::Sub' is fine. However, because I do not know the resolved values of the variables and template, I recommend that you carry out a test where the S3 URI is passed directly with resolved values in a correct format such as;

```

'Fn::Transform':
  Name: 'AWS::Include'
  Parameters:
    Location: s3://MyAmazonS3BucketName/MyFileName.yaml
```

If the test works successfully, it will help narrow down the issue to the variables not resolving properly. To further troubleshoot the cause of issue, we require details that are non-public information. Please open a support case with AWS using the following [link](https://console.aws.amazon.com/support/home#/case/create)

How to debug "Transform AWS::Include failed with: The location parameter is not a valid S3 uri."

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