Azure SQL Database – Login Failed for Newly Created User

I just created my first database yesterday. It is now set up and I can write to it from my C# application using the admin user login. I would now like to use a limited write only user so my admin credentials are not stored in my application.

I have created a second login on master using query1

CREATE LOGIN writeOnlyLogin WITH password='myPassword';

I created a user on master using query2

CREATE USER writeOnlyUser FROM LOGIN writeOnlylogin;

I then added this user to the database that has the table I want this user to write to by using query2 with a connection string targeting the new database instead of master.

I granted insert access for this user only on a single table within the new database using query3

GRANT INSERT ON myTable TO writeOnlyUser

The user has no other roles or permissions.

In my c# application I have a datastructure that I want to write to this table. I create the connection string like this and write like this. With the admin credentials the open succeeds. With my new user the open fails.

public void SendToDatabase()
{    
    string serverName = "myServer.database.windows.net";
    string databaseName = "myDatabase";
    string tableName = "myTable";
    string user = "writeOnlyUser";
    string password = @"myPassword";
    string sqlConnectionString = $"Data Source={serverName};Initial Catalog={databaseName};User id={user};Password={password};";
    using (SqlConnection sqlConnection = new SqlConnection(sqlConnectionString))
    {
        sqlConnection.Open();
        SqlCommand sqlCommand = HelperMethods.CreateSqlCommandFromObject(this, tableName, sqlConnection);
        int rowsAffected = sqlCommand.ExecuteNonQuery();
    }
}

The Exception message is, "Login failed for user 'writeOnlyUser'."

I am failing to find anything useful through google, however that could be because I don't know what I'm looking for. How can I fix this issue? In general, how can I debug login details?