GPSLarp can't start its connection
The app reports that it could not start its connection to your iPhone, and never gets as far as looking for a device.
Read the message before anything else. If it says "Tunnel is up, but no iPhone detected." then the connection started perfectly and this is not your page — that is a phone problem, on GPSLarp can't find my iPhone. Everything below is about the connection genuinely not starting, and nearly all of it comes down to the administrator prompt.
01Make sure this is the message you have
These two outcomes get confused constantly, and working on the wrong one costs an evening. They are worded differently on purpose:
- "Tunnel is up, but no iPhone detected." The connection started. The Mac looked for a phone and found none. Nothing on this page applies — go to GPSLarp can't find my iPhone.
- Anything saying the connection could not be started. Nothing was ever listening, so no phone could have been found whether one was plugged in or not. That is this page.
- A sign-in screen instead of either. Neither problem — see signed out below, because that behaviour is deliberate rather than a fault.
02What the connection is
GPSLarp does not talk to the iPhone from its own window. It talks through a small background service, and only macOS can start that service — which is the entire reason the app asks for your Mac's administrator password. GPSLarp never sees, stores or sends that password. The dialog is macOS's own, raised by the operating system; the app is handed a yes or a no. There is more on that prompt specifically on GPSLarp is asking for my Mac's administrator password.
The service listens on a local port on your own Mac, and it runs only while GPSLarp is running. That matters for what it leaves behind, which is nothing:
- No background service that persists. Closing the app stops the service the app started.
- No login item, so nothing starts itself at the next boot.
- No system extension and no privileged helper installed on the side.
That is a deliberate design choice rather than an omission, and it has one visible cost: because nothing keeps administrator rights between sessions, you are asked again next time. An app that stopped asking would be an app that had kept the privilege.
Not being asked is not a symptom
If the service is already running when GPSLarp starts — because you have used it since the Mac last restarted — there is nothing to start, so no prompt appears. That is the connection working, not the prompt going missing.
03Every way it fails
There are four, and the app words each of them differently. Match yours before doing anything.
01You were not signed in
The app refuses before it ever raises the password prompt. That order is deliberate: being asked for an administrator password and then being told you cannot use the thing it started is the wrong way round, so a signed-out user is never asked at all. If a sign-in screen is what you are looking at, start at I can't sign in to GPSLarp.
02You dismissed or declined the prompt
The message is "Admin access was not granted, so the tunnel couldn't start." Dismissing it changes nothing on the iPhone and breaks nothing on the Mac — it simply means the service was never started. Retry Connection brings the prompt back at any time.
03You left the prompt sitting there
The app waits 120 seconds and then gives up, saying the administrator prompt went unanswered. This is the one that catches people who walked away to find their password. Nothing is wrong; ask for the connection again and answer it this time.
04It started, and never came up
The password was accepted, the service was launched, and it never began listening. The app waits about ten seconds, then reports the failure, names the log file it wrote, and shows you the tail of it on screen.
This is the interesting failure, because it is the only one where the app does not know the reason and the log does. Read the tail it shows you before concluding anything — see the log below.
04The log file, which is where the real reason is
When the fourth failure happens, the app writes everything the service said to a file called tunneld.log, and it lives here:
~/Library/Application Support/GPSLarp/
01Read the tail the app already showed you
The app quotes the end of that file in the failure message, which is usually the whole answer. It does that deliberately: an earlier version named the file and stopped, and the single line explaining the failure sat in it unread while the message on screen said only that something had not come up.
02Open the file itself if you need more
In Finder, hold Option and use the Go menu to reach your Library folder, then Application Support, then GPSLarp. The log is rewritten at every start, so what you are reading is this attempt and not a history of them.
05If that did not work
The right password is refused. The prompt wants your Mac login password for an administrator account, which is not your Apple Account password. Check the account is an administrator in System Settings › Users & Groups. macOS will also accept another administrator's name and password typed into the prompt, but never a standard account's own.
The prompt is approved and immediately comes back. A previous run of the service is usually still holding on and did not shut down cleanly. Restarting the Mac clears that, and it is the one case where the unsatisfying advice is the correct advice.
Your Mac is managed by an employer or a school. A management profile can refuse administrator authorisation for this kind of request outright. Nothing in GPSLarp works around that, and no setting changes it.
The connection starts and then the phone is the problem. That is progress rather than a new fault. Two pages carry on from here: GPSLarp can't find my iPhone if nothing is detected, and My iPhone is missing a file iOS needs first if the phone is found and the app stops on a missing support file.
The app itself will not open, or you cannot find it. Different problem, one page over: The installer won't open, or I can't find the app.
The honest limit of this page: it lists the failures the app is written to report and where it puts what it knows. When the log names something this page does not cover, the log is the more reliable of the two — it is describing your Mac, and this page is describing the code.