I didn't get a notification

Something happened and your phone said nothing. There are six reasons, and three of them are the app working correctly rather than anything to fix. Working through them in the order below gets you to the right one in about a minute, because the cheap checks come first.

The six reasons, in order

Notifications blocked on this device. Your phone is refusing FriendTrack’s notifications outright, at the operating-system level. Nothing set inside the app can get past it. Open Profile → Notification Settings: if it says This device is blocking notifications, this is your answer, and the screen carries Open Device Settings to fix it. The full page is notifications are blocked on this device.
All Notifications is off. The master switch at the top of the same screen mutes every category below it. It is the one people forget, because the category they are looking at is still switched on underneath it.
The category is off. Each kind is separate. An arrival is Area Alerts; somebody starting or stopping sharing is Sharing Events; a Meeting Point being moved is Meeting Point Changes; being added to somebody’s map is Map Collaboration. Switching one off silences exactly that kind.
It was a departure. You are told when a friend arrives in an Area of Interest and never when they leave one. No setting turns that on, because it is not a setting — see arrivals, but not departures.
The Area is quiet. Whoever made the map chooses, per Area, whether arrivals there are announced. A stage may announce and a car park may not. Nothing on your phone overrides it, and it is not visible to you as a reader — the only way to know is that arrivals in one Area notify and arrivals in another never do. The creator’s side of it is announced or quiet.
It was a first sighting, or it collapsed into a batch. Two ways a real arrival produces no individual notification:
- It was a first sighting. The app noticed somebody was already inside an Area rather than watching them walk into it — which happens after the app or the server has restarted. It updates the map and announces nothing, because nobody arrived.
- It collapsed into a batch. When several people arrive in the same Area at once, the individual notifications collapse into one, reading something like 3 friends arrived → Main Stage. You did get a notification; it was about all of them.

The same six as a tree

The drawing says exactly what the six numbered reasons above say, in the same order, and the list is the authoritative version of it. The same path, written out: start from

No notification arrived

then ask each of these in turn, stopping at the first one that is true:

Notifications blocked on this device
All Notifications is off
The category is off
It was a departure
The Area is quiet
It was a first sighting

and if every one of those is false, the remaining answer is

It collapsed into a batch

A seventh thing that is not a reason, but looks like one

If you changed a setting recently and your phone had no connection at the time, the settings screen says Saved on this device, but not synced yet — these notifications may still arrive. Until it reaches the server, the server is still sending on the old setting. So the odd case is the opposite of this page: a notification you switched off arriving once anyway. Reopening the screen with a connection settles it.

Working through it, with an example

Four of you are at a festival. Somebody says they walked into the food court twenty minutes ago and you never heard about it.

You open Profile → Notification Settings. No blocking message, so the phone is not the problem.
All Notifications is on, and so is Area Alerts. So the first three reasons are out.
They walked in, so it is not a departure.
You tap the food court on the map. Two other people arrived within the same half-minute, and you scroll back to find one notification saying three friends arrived there. Reason six: it collapsed into a batch, and you did get it.

Had there been nothing at all in the tray, the remaining answer would have been reason five — the Area is quiet — and the person to change that is whoever made the map, not you.

What nobody can check for you

Whether a particular notification actually reached a particular handset is not recorded anywhere that anybody here can look at. Phones drop notifications for reasons of their own — battery savers, focus modes, a network that was down for the ninety seconds that mattered — and none of that leaves a trace on our side. So work the six reasons: they are the causes that can be established, and between them they account for nearly every report.