How do I fix this problem

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SQL-Server

i have hosted my project on the aws and its working good,but when im inserting some data that time it will showing some connection error. it is failing to connect to the database.

while im inserting im getting below error:

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 Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)

the erron is on line no:54

Line 52: cmd.Parameters.AddWithValue("@hint", txthint.Text.Trim());
Line 53: cmd.Connection = con;
Line 54: con.Open();
Line 55: userid = Convert.ToInt32(cmd.ExecuteScalar());
Line 56: con.Close();

What I have tried:

i have tried each and every solution given in google and youtube to fix this issue but my issue is remains same and it not solved yet.