aws-iot-chat-example | Chat application using AWS IoT platform via MQTT | Websocket library

CloudFormation often provides vague or hard to track errors, and never reports errors with line numbers, like many interpreters/compilers/parsers. So tracking them down is often a process of trial and error.

In your case, the error message only mentioned that the error is in the Output section of the template, but it does not mention which value is the problem. You have 6 values in that section.

A good technique for troubleshooting is to remove each of the items one or 2 at a time, and re run the template. Since the output values are just that - only Outputs - they are not needed by this template, but instead expose data to other templates later in the creation process. Just remove them as suggested, and use this technique to isolate the field with the error in the value.

A good sanity check is the remove the entire Outputs section, and confirm that the reset of the template creates as expected.

Once you track down the fields(s) with the problem, you will need to track down the primary issue: Every Outputs member must contain a Value object

To resolve that, track down the object being referenced, and track back to the source resource or resource attribute. For some reason, those references do not refer to a valid object.

I will note that in your comments, you identified two fields that were both causing the error. Both seem to use a variable reference in the form of self:custom.variables.google_app_id - These value are not resolving properly. Check their source as above. I suspect they are not being parsed properly. I do not recognize that construction as valid CloudFormation syntax.