ZTE Max N9520 – How to insert unlock code?

Please HELP ME how to insert unlock code for unlock this smart phone.

ZTE Worldwide Unlock Codes

My ZTE MAX is from Sprint BOOST operator.

I insert an unacceptable SIM card to phone, not ask me the unlock code.

Insert Tmobile SIM card, insert PIN code, phone not have signal, and in info operator write "invalid SIM card/Boost Mobile"