We recently encountered the issue described here - Unable to create Project, key already exists
Can I suggest that you improve the error message so that it includes the information in the post I’ve linked to? e.g.
if its in your org -
Could not create Project, key already exists in your organization: {project-key}.
if it’s outside your org -
Could not create Project, key already exists outside of your organization: {project-key}. Project keys are global in SonarCloud.