Unable to retrieve StoreId via GetBMCStoresByCustomerId
I'm attempting to set up shopping campaigns by using the Bing Ads API Python library. I have no problem authenticating and creating a campaign service object that will carry out most any add/update operations I ask it to do -- updating budgets, pausing and enabling campaigns, etc. -- but when I attempt to run GetBMCStoresByCustomerId to get the StoreId value for a given account, I consistently get a 106 suds WebFault error: "The user does not represent a authorized developer." Does running this particular service operation require a different level of developer access than the other API actions I'm describing? I've tried following the structure of the examples in the GitHub depository and nothing seems to fix the issue. Thanks in advance for any insight you can provide.