I've installed SQL Express on my PC hoping to do some practice creating tables and then modifying them. I coded a webpage in Visual Studio to, basically, SELECT * from a table in the SQLEXPRESS, but I can never get the connection string to work. Please help

My connection string

"Data Source=localhost\SQLEXPRESS;Initial Catalog=test;User Id=xaa9-PC\xaa9;Password=abcd;"

Error Message:

Query is select * from tblCustomers where username='johndoe' error is Login failed for user 'xaa9-PC\xaa9'.