Jiggy-Ninja:
What is the mySerial instance? Is it SoftwareSerial?
Yes, it's instance of SoftwareSerial.
PeterH:
It looks as if you're trying to use the varargs vprintf style formatting when printing to a stream. That won't work. You need to either use snprintf() or similar to format the string to a char array and then print the resulting string to the serial port, or write the fixed text and the variable decimal number in separate calls to serial.print. Since there's only one variable, the second approach would seem more sensible.
Well, it's only one variable in this example but actually there's going to be more variables (more post request parameters).
So maybe first approach could work better. I hope I'll make it work like that, I need to study C++ syntax better.
Thanks