You are receiving a 401 error due to an authentication failure. You want to make sure that for the username field you are inputting your API key and username separated by a '%'. EX: fb01f979-XXXX-XXXX-XXXX-XXXXabcd1212%joesflowers
Once you have the correct login information you should be able to retrieve collection information from the URI.
Support Engineer, Constant Contact
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