I wrote this earlier, so I could send it through to you.
Rather than letting it go to waste, here it is.
So you are obviously aware the NExT has 2 chips in it.
An HF that you can write to with your phone and an LF that you can write 2 with a special tool.
Let me break them down for you a little more
Firstly, don’t worry about the password, think of it more like an “anti fuck up my implant protection system from myself and others”
With your phone, I don’t want to insult you, but it is always easier to start with the basics just to make sure we are singing off the same song sheet. So no insult meant.
Make sure your NFC is turned on
phone unlocked
Remove cover if it has one
Use your diagnostic card
on the back to make sure the NFC is working ( The HF LED should flash )
Then use your xFD
and move it slowly on the back of your phone in all different orientations, You are looking for the Brightest light ( Not unusual for your LED to pulse with a few low power flashes then a High power )
When you have found the best orientation, that is what you want to replicate with your NEXT.
If you have an iPhone, then same applies but it will be your top edge you will be using, To read you will place it like a 
across the NExT
Where and how are you trying to scan it?
Have you checked the phone compatibility list ( Dont worry if it is not on it, but if it is on there , it may give you some helpful pointers )