SQL Query CASE Clause when > 180 days between TransactionDate for same MemberNumber

probably a simple request but a rookie like me can't seem to figure it out.

I just need a query that generates results when there is > 180 days between the TransactionDate for each MemberNumber. This is what I have so far but it's not working correctly:

SELECT [TransactionDate]
  ,[MemberNumber]
  ,[MemberName]
  ,[PrincipalAmount]
  ,[TransactionCategory]
  ,[TransactionChannel]
  ,[Service]
  ,[Product]
  ,
  
CASE 
WHEN DATEDIFF(day, TransactionDate, TransactionDate) > 180 
AND MemberNumber = MemberNumber THEN 'Dormant'
ELSE 'Active'
END AS Dormant_Flag

Using Lag() you can obtain the previous Transaction date for a MemberNumber

SELECT [TransactionDate]
  ,[MemberNumber]
  ,[MemberName]
  ,[PrincipalAmount]
  ,[TransactionCategory]
  ,[TransactionChannel]
  ,[Service]
  ,[Product]
  , LAG(TransactionDate) OVER (Partition BY [MemberNumber] ORDER BY TransactionDate) as PreviousTransactionDate
  ,DATEDIFF(Day, LAG(TransactionDate) OVER (Partition BY [MemberNumber] ORDER BY TransactionDate) , TransactionDate) as diff
  
,CASE 
WHEN DATEDIFF(Day, LAG(TransactionDate) OVER (Partition BY [MemberNumber] ORDER BY TransactionDate) , TransactionDate) > 180 
THEN 'Dormant'
ELSE 'Active'
END AS Dormant_Flag
FROM Example

fiddle