Want to Activate The ATF JTAG

Dears ,

I have ATF Nitro and want to activate it.

When i select the ATF Store i found that ATF JTAG Credit $ 39.00 USD

I want to know how much credit i will gain after paying the 39$ ?!

How much credit i need to repair a phone using the ATF Jtag Tool ?!

Can i fix boot for Lumia XL runs Android

Many Thanks and waiting for your feedback to proceed with the activation.