Decode Function , returning bad data

hello i m trying to decode payload to get temperature value but after doing mathematical operations i did not get the good value , the problem that when i convert payload from text to decimal and do mathematical operations manually , i get the good value but , the issues that by default the payload is in base64 so i search for solution to get payload in text format instead of base 64 , thank you in advance …
note ; the data in this example is “f2iao4o=”

I’m not sure if I understood your question correctly. You’re looking for a way to change the format of the payload given by the App Server from Base64 to another format? . As far as I know, the payload is in Base64 by default and you can’t change it. That leaves your final app to make the formating.
If you use C++ in your app you could use Boost or Cpp-Base64 Lib