Hello Camcam,
the NFC loop is built identically to the model 8. The important thing is why it stopped working. Immediately before noticing that NFC is not working, did your phone have a fall or similar incident? All this, from the point of view of diagnostics, is important and speeds up the whole process.
The antenna problem never occurs by itself. It is usually related to a fall or wather damage. In fact, all you can do (assuming you have experience with a screwdriver) is to remove the screen and check the continuity of the antenna line from the motherboard to the internal antenna at the top of the housing. In case of an incorrect reading, you can replace the 1-st step antenna. The cost is about $2-5 if you decide to do it yourself. On the other hand, you can test ApplePay in store when paying before and after factory resetting your phone. Sometimes it happens that NFC communication hangs the entire subsystem due to compatibility problems with various devices in this technology. The third and final option is to find a good repair shop where the technician "took his teeth" (or "ate his teeth" - people say that in my location) on repairing the motherboard of Apple devices. You're sure to find a few of these places depending on your location.