How to Insert JSON data to BYTEA column in the table in POSTGRESQL?
There is no reason to convert anything, just insert the JSON strings (after making them valid JSON):

CREATE OR REPLACE FUNCTION INS_BLOB() RETURNS VOID AS $$
BEGIN
 INSERT INTO "TBL1" ("SN","COL1","COL2") 
 values(1, 
    '{
      "APPLICATION": {
         "MEMORY": {
         "OPTIONS" :{
                      "SOMETHING" : "SOMETHING",
                      "format" : "SOMETHING",
                      "System" : "",
                      "IP" : "",
                      "Port" : "",
                      "template" : "",
                      "Path" : "" ,
                      "Name" : "QUEUE",
                      "URL" : ""              
        }}}}', --&lt;&lt; add the missing curly braces!
     '{
      "APPLICATION": {
       "MEMORY": {
       "OPTIONS" :{
                "SOMETHING" : "SOMETHING",
                "format" : "SOMETHING",
                "System" : "",
                "IP" : "",
                "Port" : "",
                "template" : "",
                "Path" : "" ,
                "Name" : "QUEUE",
                "URL" : ""  
        }}}}'); --&lt;&lt; add the missing curly braces!
END;
$$
LANGUAGE plpgsql;
COMMIT;




You also don't need PL/pgSQL for this. A language sql function would be enough (you would need to remove the begin and end though)