Got this error out of the blue Microsoft.Data.SqlClient.SqlException (0x80131904):

Question

Microsoft.Data.SqlClient.SqlException (0x80131904): A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL

Answer 1

As the message already says, verify that the SQL Server is running. See https://learn.microsoft.com/en-us/troubleshoot/sql/database-engine/connect/resolve-connectivity-errors-overview

Answer 2

connectionstrings :{
 //"CasePortal": "Server=database-sjhfishf.ctvuprpbyvso.us-east-
    "CasePortal": "Server=mydatabase-hscksckn.ctvuprpbyvso.us-east-  }

Thanks for help. just by adding mydatabase instead of database the issue was resolved