DataSet query: unauthorized?

I'm trying to use the 'query' endpoint of the DataSet API but I'm getting an Unauthorized response. Not sure if I'm formulating the query incorrectly or if I need to adjust permissions within Domo. (So far this problem has been specific to querying -- I can programatically list, retrieve, and export datasets just fine. All the tests in the gem I'm building pass except test_query_data.)

My code is sending a POST to /v1/datasets/query/execute/<dataset_id> and is getting a 401 response with the message:

com.domo.bedrock.service.exception.UnauthorizedException: Full authentication is required to access this resource

Each 401 response also has an attribute named 'toe' with what looks like a unique incident ID. I can post one of those here if a Domo employee is reading and could do anything with it.

I've tried a few different SQL queries in the payload of the POST:

• select * from table <-- this matches the API reference example
• select count(*) from table
• select * from `API Test Data` <-- this is the name of the dataset I'm testing against 
• select count(*) from `API Test Data`

But the response is the same no matter what. Anyone know what I'm doing wrong or how I might troubleshoot further?