How to change "Item number" field on paypal paymant page.
I am having a very long item number on paypal payment page like this - M3wzfDR8YTBBMlpWS0hkaERiSXxybFBheUFzWW91R29DcmVlVH JhbnNhY3Rpb258ZW58cGF5QXNZb3VHb0Ny
It's happening when the customer is buying credits through "Pay As You go Credits".(Refer Attached - SnapShot1) This doesn't have any meaning. So I want to change it something meaningful like "Buying credits plan1"
And also it is appearing on paypal invoice email as well. It is confusing the customer. (Refer Attached - SnapShot2)
That number is not generated by paypal they are getting it from our Flynax software.
Please tell me how to change it? Which file and line that I can find that number in root directory?