Cura - Printer does not accept commands

What is the problem?

When I go to the MONITOR tab in Cura 4.1, it says "Printer cannot accept commands". Clicking on Print with Octoprint says "Printer is offline" and asks to queue the job.

What did you already try to solve it?

Rebooted the octoprint, checked the cable connection, swapped the USB cable for a "known good one"

Logs (octoprint.log, serial.log or output on terminal tab, browser error console ...)

How do I get these?

Additional information about your setup (OctoPrint version, OctoPi version, printer, firmware, browser, operating system, ...)

Latest Octoprint (Version 1.3.11), Cura 4.1.0

You might want to visit the configuration for that in Cura and verify that the API key was entered correctly.

Just click onto the blue text Logs.

Is your printer accessible from the web interface?