I keep getting the following error message, even after trying in 3 new playgrounds: 
Challenge Not yet complete... here's what's wrong: 
Some billing state names do not meet data quality standards, or the data import was unsuccessful.

I followed all of the instructions:
1. Installed unmanaged package in the new playground
2. Added Residential picklist type to Accounts
3. Cleaned up Account list:
a. Removed "Household" from Account name (this wasn't specified, but it didn't seem necessary)
b. Removed duplicate records
c. Changed accounts in ALL CAPS to only cap first letter of first and last name
d. Changed state name to 3 letter State code
e. Saved as .CSV file
4. Imported list using Import Wizard

I received an email confirming the import was successful with 11 rows processed and I see the accounts when I search up accounts in the playground. 

Thanks in advance for any help!