If your reMarkable is stuck showing “sync failed” and a force sync returns the message “content transfer failed 400”, you’re dealing with one of the more cryptic errors the device throws up. The good news is that this error has several known causes, each with a straightforward fix. The bad news is that it’s not always obvious which cause applies to you.
Here’s a breakdown of every solution the community has found to work, starting with the simplest.
Fix 1: Close the File You’re Trying to Upload
This is the most common cause and the easiest fix. If you have a PDF or document open on your computer while trying to upload or sync it to your reMarkable, the transfer will fail with a 400 error.
Close the file completely, then try the sync again. Multiple users have confirmed this resolves the issue immediately. It’s worth trying before anything else.
Fix 2: Update Your reMarkable Device Software
An outdated firmware version is a frequent trigger for this error, particularly after reMarkable pushes a server-side update that requires a matching device version to sync correctly.
To check for and install updates on your reMarkable:
- Open the menu on your device
- Go to Settings
- Select Software
- Tap the arrow and choose Check for Updates
Install any available update, then attempt the sync again. Several users have resolved the 400 error this way, including those who had left their device unused for an extended period.
Fix 3: Update the reMarkable Desktop App
If you’re seeing the “network failure 400” or “content transfer failed 400” error in the reMarkable Mac or Windows desktop app rather than on the device itself, the desktop app may be out of date.
Update the app via the Mac App Store or by downloading the latest version from reMarkable’s website, then try syncing again. At least one user resolved the error immediately after updating the desktop app.
Fix 4: Restart the Device and Wait
Sometimes the error is caused by a temporary issue on reMarkable’s cloud servers rather than anything wrong with your device. In these cases, the sync will fail regardless of what you try locally.
Restart your reMarkable and put it aside for 20 to 30 minutes. Some users have found the sync resolves on its own after a couple of restarts and a short wait. If reMarkable’s servers were the cause, the error will clear without any further action on your part.
Fix 5: Scroll Through the Document Before Syncing
This one is less intuitive but has been reported to work in some cases. Before attempting the sync or upload, open the document and scroll through it page by page to the end. Then close it and try again.
It appears to work similarly to Fix 1: fully loading or closing the document on the sending side before initiating the transfer.
Fix 6: Fix a Time Signature Sync Issue (for Persistent Cases)
If none of the above work and the error has persisted for a long time, particularly on older reMarkable devices, the issue may be caused by the device’s internal clock being out of sync. This is more common on devices that haven’t been used or updated for a long period.
Here’s the process that has worked for users with this issue:
- Download the reMarkable desktop app if you don’t already have it
- Connect your reMarkable to your computer using a USB cable (not wireless)
- On the device, go to Settings and turn off Auto Sleep and Auto Power Off
- Keep both your computer and your reMarkable awake and active for up to 45 minutes
- At some point during this window, the device will self-correct its time signature and a sync should complete
This method is a last resort for persistent cases, but it has resolved the issue for users who had tried everything else.
Quick Reference: Which Fix to Try First
| Situation | Start here |
|---|---|
| Just bought the device or recently set it up | Fix 2 (update firmware) |
| Failing on a specific file | Fix 1 (close the file first) |
| Error appears in the desktop app | Fix 3 (update desktop app) |
| Started happening suddenly with no changes | Fix 4 (restart and wait) |
| Device hasn’t been used in a long time | Fix 2, then Fix 6 |
| Nothing else has worked | Fix 6 (USB time signature fix) |
Still Not Syncing?
If none of the fixes above resolve the error, the next step is to contact reMarkable support directly at support.remarkable.com. When you reach out, include your device’s software version, which sync method you’re using (wireless or USB), and a description of when the error first appeared. This gives their team the information they need to diagnose your specific case quickly.
For more help with your reMarkable, browse our full e-ink troubleshooting guides.