My iPhone is missing a file iOS needs first
GPSLarp stops before it reaches your phone and says "Your iPhone is missing a support file iOS needs first." Or the setup check shows a card headed "Your iPhone needs one more file from Apple" with an Install button under it.
Press Install. The file is Apple's, it comes from Apple, and GPSLarp fetches and mounts it for you — which is why the card has a button rather than instructions. It needs an internet connection. It does not need a restart, and it does not need your Mac's administrator password.
01What the file actually is
It is called a Developer Disk Image, and it is a small package of developer-side services that Apple publishes for each iOS build. Until one is mounted, the phone simply does not offer the services GPSLarp drives — the same ones Xcode uses. Not "refuses them": does not advertise them at all, which is why the failure reads as the app talking to a phone that is present and unhelpful.
Two properties of it are worth knowing, because both surprise people:
- It is matched to the exact iOS build. Apple publishes one per version, and a phone on a version Apple has not published one for yet has nothing available to mount. GPSLarp says so in those terms when it happens.
- It is not part of GPSLarp. Nothing in the app ships it and nothing on this site hosts it. The app asks Apple for it on your behalf and hands it to the phone.
02Why it comes back after a restart
The image is mounted for the session. Restart the iPhone and it is gone, and the next thing that needs it has to mount it again. That is iOS's design rather than anything failing.
It is also the answer to the most confusing version of this problem: you set a location yesterday, restarted the phone overnight, changed nothing at all, and this morning GPSLarp says a support file is missing. Nothing broke. The restart cleared the mount, exactly as it always does.
So this is not a one-off setup step
Developer Mode is a switch you flip once and it stays on. This is not that. It is closer to a thing the app does for you at the start of a session, and the reason you ever see it is that the app tells you rather than doing it silently — the file comes from Apple over your connection and lands on your phone, which is not something to do behind somebody's back.
03Let GPSLarp install it
01Check this Mac is online
The file is downloaded from Apple during this step. A Mac with no connection cannot complete it, and neither can one sitting behind a Wi-Fi login page it has not been through yet.
02Leave the iPhone plugged in and unlocked
The mount goes to the phone over the connection you already have, so the phone has to be reachable and unlocked while it happens. If it is not, the app reports the lock or the pairing rather than this — see GPSLarp can't find my iPhone.
03Press Install and wait
The button is on the card itself, labelled Install it now. It usually takes under a minute. Nothing on the phone is restarted and nothing is added as an app.
04Run the check again
The setup check re-runs and moves on to the next thing it looks at. If it still reports the same file, go to If that did not work below.
04What this message tells you about Developer Mode
Something useful, and it saves people an afternoon: the check for this file runs after the check for Developer Mode. A phone with Developer Mode switched off is stopped by the earlier check and never reaches this one.
So if you are looking at this message, Developer Mode is already on. You do not need to go and check it, and you should not go and toggle it — turning it off restarts the phone, which clears the mount you are trying to create. If you have not been through that switch at all yet, it is on Developer Mode isn't showing on my iPhone.
05If that did not work
The Install step failed and mentioned the connection. This is a download from Apple, so it fails the way downloads fail. The three that account for nearly all of it:
- A captive Wi-Fi portal — a cafe or hotel network the Mac has joined but not signed in to. Web pages redirect; this does not.
- A corporate proxy or filter between the Mac and Apple. Trying the same thing on a home or phone-tethered network settles whether that is it in about a minute.
- No usable connection at all, including a VPN that is up but not passing traffic.
The phone was restarted between the check and the install. Run the check again before pressing Install. The check is describing the phone as it was, and after a restart that description is stale in exactly the way this page is about.
It says Apple does not publish an image for this version of iOS yet. Then there is nothing to install and nothing to configure — that is a gap at Apple's end, usually on a very new release or a beta. Waiting is the only move, and it is worth reading Will GPSLarp work with my Mac and my iPhone? before assuming anything else about your version.
The app never gets as far as this card. Then the problem is upstream of it: either the phone is not being found at all (GPSLarp can't find my iPhone) or the connection itself did not start (GPSLarp can't start its connection).
The honest limit of this page: it describes what iOS requires and what the app attempts. Nobody here has watched this step succeed against a real phone, so what is written above is the requirement and the mechanism rather than a report of it working. If you get an outcome this page does not predict, the page is the thing that is wrong.