Syntax for default value in Use Custom Metadata Types in Formulas, Default Values, and Validation Rules?

Exercise in first section "Default Values" - when I fill in the value indicated here, it results in a syntax error.  Following the advice of the note below, I tried adding some suffixes (like "Support_Tier__c" but syntax error persists. 

For Default Value, type: $CustomMetadata.Support_Tier__mdt.Bronze.MasterLabel

Now when you create an Account record, the default value, Bronze, appears in Support Tier.Click Next, Next, and Save.

There’s no UI for the Default Value option, so you can’t use the editor Select and Insert options when creating a custom metadata default value. The syntax is: $CustomMetadata.CustomMetadataTypeAPIName.RecordAPIName.FieldAPIName. Use the correct suffixes. For the custom metadata type, use __mdt. For fields, use __c. Records don’t require a suffix.

#Trailhead Challenges