Could not connect to Prusa Connect: HTTP 401: Missing or invalid API key  

RE: Could not connect to Prusa Connect: HTTP 401: Missing or invalid API key

I've forgotten the information:

MK4 printer

slicer: version 2.7.1+win64

RE: Could not connect to Prusa Connect: HTTP 401: Missing or invalid API key

I tried it on another computer and it worked there.

I tried reinstalling slicer -> it didn't help.

I removed the physical mk3 printer that had the settings to send to octoprint.

And then mk4 works 🙂

Obviously mixing settings from multiple printers 🙂

So, solved for me 🙂

RE: Could not connect to Prusa Connect: HTTP 401: Missing or invalid API key

Huh, you were faster than my forum checking frequency. Good job figuring it out tho.

RE: Could not connect to Prusa Connect: HTTP 401: Missing or invalid API key

I have the same "Could not connect to Prusa Connect: HTTP 401: Missing or invalid API key" issue with PrusaSlicer 2.7.4 and my MK4 on firmware 5.1.3+13503.

It worked for a few months and stopped suddenly (after I updated either the firmware or PrusaSlicer, I cannot recall), but I switched to PrusaLink and worked with it.
However, now I have to start large print jobs, and it takes ages to upload even bgcode to PrusaLink.

I also have MK3 printer profiles, which are not mixed with the MK4 ones. Anyhow, that shouldn't be a breaking issue, and PrusaSlicer should discriminate correctly.

Is anyone else having that issue?

Cheers,
Martin

RE: Could not connect to Prusa Connect: HTTP 401: Missing or invalid API key

For testing, I removed all other printers but one MK4 from PrusaSlicer, but I still get the same error.

RE: Could not connect to Prusa Connect: HTTP 401: Missing or invalid API key

I had to remove the MK3 connected to the octoprint, after restarting slic3r it worked as it should.

RE: Could not connect to Prusa Connect: HTTP 401: Missing or invalid API key

The duplicate button is in the three dot dropdown. Yes, I agree that we are missing a UX person. That is one of the things I said first year I was working here. (I have been introduced to ux and its testing at uni). I believe things will improve tho

RE: Could not connect to Prusa Connect: HTTP 401: Missing or invalid API key

For anyone else who finds this, I had the same issue with 2 printers but didn't want to delete them.  I found that I had PrusaLink configured for both printers but it was using "HTTP Digest" as the authentication method (which worked fine to upload directly to PrusaLink on each printer).   I changed this to 'API Key' and then changed the Host Type back to PrusaConnect and entered the PrusaConnect API key and it was able to connect to PrusaConnect correctly.  Seems like a bug where the PrusaConnect window is incorrectly using the authentication method info from the PrusaLink window, even though PrusaConnect doesn't support HTTP Digest authentication through PrusaSlicer.

RE: Could not connect to Prusa Connect: HTTP 401: Missing or invalid API key

Thank you for this. It stopped working and I couldn't figure out why. Your post got me back up and running again. Cheers.

Posted by: @kevin-20

For anyone else who finds this, I had the same issue with 2 printers but didn't want to delete them.  I found that I had PrusaLink configured for both printers but it was using "HTTP Digest" as the authentication method (which worked fine to upload directly to PrusaLink on each printer).   I changed this to 'API Key' and then changed the Host Type back to PrusaConnect and entered the PrusaConnect API key and it was able to connect to PrusaConnect correctly.  Seems like a bug where the PrusaConnect window is incorrectly using the authentication method info from the PrusaLink window, even though PrusaConnect doesn't support HTTP Digest authentication through PrusaSlicer.

RE: Could not connect to Prusa Connect: HTTP 401: Missing or invalid API key

I had no idea why my MK4S started showing erratic behavior with PrusaConnect (crashing file transfers, not showing online). 

Turns out I had the parameter also set to PrusaLink as you described, I switched the settings to PrusaConnect API and now not only is the problem solved but file transfers to the printer are much faster. 

Thanks a lot for the help.

Posted by: @kevin-20

For anyone else who finds this, I had the same issue with 2 printers but didn't want to delete them.  I found that I had PrusaLink configured for both printers but it was using "HTTP Digest" as the authentication method (which worked fine to upload directly to PrusaLink on each printer).   I changed this to 'API Key' and then changed the Host Type back to PrusaConnect and entered the PrusaConnect API key and it was able to connect to PrusaConnect correctly.  Seems like a bug where the PrusaConnect window is incorrectly using the authentication method info from the PrusaLink window, even though PrusaConnect doesn't support HTTP Digest authentication through PrusaSlicer.

RE: Could not connect to Prusa Connect: HTTP 401: Missing or invalid API key

How/where do I change it to 'PrusaConnect API key'? On the printer? Prusa Slicer? Prusa Connect tab in slicer? Can't find it anywhere

RE: Could not connect to Prusa Connect: HTTP 401: Missing or invalid API key

2025 and this glitch is still present. Thanks for the help 🙂

RE: Could not connect to Prusa Connect: HTTP 401: Missing or invalid API key

Thank you so much as well; this is in no way shape or form an intuitive fix.  This should be a banner on the prusaconnect page if they aren't going to bother fixing their apps.   It has been over a year and this is STILL an issue, i am embarrassed on Prusa's behalf.

RE:

Bug Recap

Observed: Physical Printer Print Host Upload settings in PrusaSlicer are shared between different host types. All attributes are common to all host types, even where they do not apply. The active host upload configuration may be affected by settings that are not valid for the active host type, and not visible in its configuration form.

Expected: Physical Printer Print Host Upload settings in PrusaSlicer should be specific to the host type. Changing values in one host type should not affect another host type. Invalid or inapplicable settings should not be applied from other host types.

Consequences

1. Upload configuration attributes may be applied where they are invalid (e.g. "Authorization Type" for PrusaConnect).
2. Users who previously used PrusaLink with HTTP Digest authentication receive "HTTP 401: Missing or Invalid API Key" when trying to configure PrusaConnect.
3. It is not possible to have (for example) a valid PrusaLink host upload configuration and a valid PrusaConnect host upload configuration stored in PrusaSlicer simultaneously, and easily switch between host upload types.

Workaround for PrusaLink to PrusaConnect reconfiguration

1. Open Physical Printer settings.
2. Edit PrusaLink settings.
   1. Change the authentication method to API Key.
3. Edit PrusaConnect settings.
   1. Set the "Hostname, IP or URL" field to https://connect.prusa3d.com.
   2. Set the "API Key / Password" field to your Connect API key.
   3. "Test" connection button should now work.

Thanks to @kevin-8 for characterizing the issue.

I am not a Prusa employee. I am merely a user annoyed by this bug and grateful for a workaround. If anyone wants to copy this over to GitHub and make it a "real" bug, they have my permission.