Hi. kindly help me cross check what seems to be the error here. I want to pass an input string value to "msg.text" variable and i want it to write on mySQL database. my "msg.payload" works fine, the issue lies only on the "msg.text".

Does msg.text actually have a value?
Use a debug node (set to show complete msg) BEFORE the function node.
OR
add node.warn(msg.text) in your function BEFORE setting msg.topic
Lastly - it is strongly recommended you use prepared queries / parameters instead of generating a SQL Query string (it is unsafe / prone to SQL injection) - read the node-red-node-mysql help to see how to use parameters.
this "msg.text" takes in the string character from whatever i input on the dashboard. I tested on a separate flow and this works fine. but this problem arises when i try to included it in the query.
I tried changing the debug node to display "all msg object" and i manage to get the msg.text data as "a" string value.

This time yes, but your first error was different - it showed undefined so I can pretty much guarantee msg.text was NOT present.
this time you have a different error and it is coming from a different node (i can see this one is named sends_data_to_SQL where as the previous error came from an unnamed node).
For reference: toFixed only works on numbers (you must be calling toFixed on a string or something else inside sends_data_to_SQL). Use the same tips I showed you previously to determine what that is.
i only called ToFixed() for msg.payload which is a number. and it works as shown.
sends_data_toSQL is basically a function node which contains the query as shown in the image above.
hi. So sorry, i will try to attach my whole flow here next week. office is closed on weekends.