Regarding payment with an xNT @Ima_Wana_Be has given you the answer with the link to follow, as things stand now!
However I would also add
on the near horizon, and recently revealed to us, there is a new product line that will have “PROPER/ ACTUAL/ REAL/ LEGIT/FOR TRUE-SIES” payment capability. ( eventually - think fitted for, but not with…) It is a part of the Vivokey line of products, and they will be called Vivokey Apex.
here is the informal / unoffical announcement
To answer your other question,
You will see below, things are not always black and white 
and I will use words like NORMALLY/ GENERALLY/ OCCASIONALLY there are exceptions to the rules SOMETIMES 
The xNT is a great little implant and ontop of using it like you currently are, you can also use it for things such as access to work and/ or home and/or school or transit/travel ( though travel are NORMALLY quite locked down). The caveat is, it also depends on the compatibility of the xNT with these access systems.
There are plenty of people on here that can help you with this, but we would need a little more information about the systems you are trying to use it on.
GENERALLY
Access systems just look for a unique ID(UID), of which your xNT will have one. As long as it is compatible, if you own it, it is easy to enroll, if you don’t, this is often where some social engineering comes into play.
Before we go any further, I am not sure of how much knowledge you have in this area, but I would suggest you read through some of this forums Wikis.
Basically there are 2 main frequency types:
Low Frequency (LF) 125kHz - The UIDs can often be copied / cloned and written to - they are less secure but very abundant in the big wide world 
High Frequency (HF) 13.56MHz - These can RARELY have their UIDs copied / cloned and written to - including your xNT - Dangerous Things sell the xM1 ( Soon the xM1 Flex??? or similar name ) which is an HF implant with a changeable UID, BUT, is only compatible with specific systems.
Included in the HF space is NFC which your phone will LIKELY have.
As you would have found, you can easily write NDEF data to your xNT and change this as much as you would like, business cards, plain text etc. using NFC tools or similar.
I am trying to keep it simple AND give you as much info as possible. After reading the Wikis, it should hopefully be making sense
Anyway
Now for some projects, if you search Amazon, ebay, aliexpress, wish, banggood etc. and type in 13.56MHz locks you should find a bunch of door lock / draw locks that operate on these frequencies, ( which can be repurposed to other projects,) the cheap chinese one will MORE OFTEN THAN NOT work with your xNT, what you are looking for if it is listed is:-
13.56MHz
ISO14443A
Arduino as another path you can take and Dangerougs Things sell some components for this
Thing one : Thing two
You can also use you xNT as a way to unlock your laptop / computer with a simple “plug and play” kbr1 reader
to further your
I would suggest for you, to get some information for any access systems you use, and provide us as much detail as possible and we can hopefully point you in the right direction for a compatible implant. Hopefully the xNT you already have. 
I always recommend the NExT because of its multifunctionality, it has the same xNT that you have PLUS an xEM, in your case you COULD just get an xEM, BUT I would still suggest a NExT…OTY
the beauty of the xEM / NExT is it will open 
a world of very common LF devices / systems / projects.
Do the same as I suggest above for searching Amazon, ebay, aliexpress, wish, banggood etc. but type in 125kHz locks.
When you own a “thing” you can NORMALLY easily enroll an implant to it and use it just as easy.
When you go to get some more devices, dont forget to plan for the future as to what you want to put where!
That should be enough to digest for now.
Good luck