Error with Power Query Merge After Close & Apply....

[ACECEO]

I am new to Power BI and am having an extremely hard time creating a simple report. 

I have three tables. 

1. Policy
2. Account
3. Member

The Policy Table contains a Column named policy_holder_name_id which connects to the account_id on the Account Table. 

Each Policy can have Exactly One Policy Holder, so I believe that's Many to 1 because the same Account can hold multiple policies. 

The Member Table contains a column named parentcustomerid which connects to the account_id on the Account Table.

Each Member can have exactly one Parent Customer ID, so I believe that's Many to 1 because the same Account can hold multiple members. 

I set up Accout and Policy or Account and Member fine. 

However as soon as I try to add in a field from the 3rd table, I get an error. 

 If I was using SQL, I'd use temporary tables, one containing Policy and Account and the other containing Member and Account, and then I would left join Account ID on Account ID and be done with it. 

It seems the pathway to resolution may be with Power Query at the DataSet level via merge per the article below https://learn.microsoft.com/en-us/power-query/merge-queries-left-outer

I seem to have successfully merged the tables in accordance with what I'd do in sql. 

However, when I click Close and Apply and return to the normal enviornment I get the error below. 

Any guidance, recommendations, direction, or assistance you can provide would be greatly appreciated. 

[ACECEO · Accepted solution]

This was the fix - https://community.fabric.microsoft.com/t5/Desktop/Query-references-other-queries-or-steps-so-it-may-...