You get an error message that the project can’t be saved.
Is this a debugging issue or a troubleshooting issue? Put your answer and your reasoning in a comment.
This is a troubleshooting issue (there may not be anything wrong in the code) .
Your internet connection may have been interrupted.
The project you are trying to save may be open on another computer or in another tab in your browser. Close the other tab or browser. Remix the project to see if you can save a copy of it.