Microsoft.Data.SqlClient.SqlException (0x80131904) asp.net core3 two databases code example

Example: asp.net core web api Microsoft.Data.SqlClient.SqlException (0x80131904):

"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