How can I upload mp3 file in binary format on AppInventor?

Which way do you want to transfer?

App > Server or Server > App

App to a Server

Use the web component and the post file block. Your server may need some request headers....

Yes I used it, but I am getting "not found" as response instead of a valid json!

Are you able to transfer a file using postman or curl ? If so what is this syntax you are using for that?

Otherwise show example of the url path, parameters and headers you are sending.

Here a simple example with php

Oh the response needs to be decoded using the webComponent.JsonTextDecodeWithDictionaries block!

Thanks for taking out the time to respond!