The login is from an untrusted domain and cannot be used with Windows authentication.
It would help if you used Windows Authentication. One of the next things needs to be true:
1. You execute from the same machine as the database server.
2. You have an Active Directory environment. The user you execute the application under, and you have the right to connect to the database.
If the conditions above are not true, you need to:
1. Establish a Windows Domain Controller, connect all the machines to the controller, fix SQL server to use domain accounts, or
2. Change the SQL server to use both Windows and SQL Server accounts.
The easiest way is to change the SQL Server to use both Windows and SQL server accounts. Then you must create a SQL Server user on the database server and change your connection string. The first option will take a day of installation and configuration. The second option takes about 5 minutes.
It is possible to have the connection string username and password overwritten with the Windows login and password. Integrated security means to use your Windows credentials for login verification to SQL Server. If you are logged in to another domain controller, then it will fail. You need to use:
IntegratedSecurity = false;
Now, SQL Server will use the SQL Server login and password provided in your connection string. The SQL Server instance needs to have its authentication mode configured to mixed mode, the SQL Server and Windows Authentication mode. To check or change this SQL Server Management Studio setting and right-click on your server name and select Properties. On the pop-up, choose security, and you will see where you need to alter the setting if you need it.