Error 400 when queueing a new file when the printer is offline  

Error 400 when queueing a new file when the printer is offline

Issue description

At the moment, if my printer is offline, it is not possible for me to queue new prints from PrusaSlicer.

The prints are successfully uploaded to Connect, but they are not added to the printer's queue. In addition, an ugly error message is displayed in the slicer, both as a popup and a notification.

It would be beneficial to allow people to queue files even if their printer is offline, and then the printer can fetch the queue whenever it is online again.

PS: From an API design perspective: HTTP error code 400 (bad request) is the wrong code to respond in this case. The client didn't do anything wrong; maybe 409 would be more appropriate?

Steps to reproduce

• Turn off printer, make sure it is in state OFFLINE in Prusa Connect.
• Slice a file, and use the "Send to printer" button to queue the bgcode in Prusa Connect.
• Admire the beautiful error message.

What would you expect instead?

I expect the file to be queued in Prusa Connect without an error.