Check out example codes for "asp.net core web api Microsoft.Data.SqlClient.SqlException (0x80131904):". It will help you in understanding the concepts better.

Code Example 1

"ConnectionStrings": {
    "DefaultConnection": "Server=192.168.1.XXX\\SQL2012; Initial Catalog=IBCOREDB_XXX; User ID=XXXX;Password=XXXXX;",
  },

// check the connectionString if it's correct sometimes it can lead to an connect error

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