Can't save to the cloud
You're not signed in
Cloud save needs an account. Sign in first: see Signing in. You can always Save to this computer (.vemb)… ("Download (.vemb)" on the web) without an account.
"You've reached the design limit"
The Free plan keeps up to 10 designs in the cloud. When you hit it, Boldbobbin shows your count and the cap and offers to Upgrade to Pro or delete some designs. You can keep working and save to your device in the meantime.
To free space, open My designs and delete designs you no longer need (deleting can't be undone). Pro gives unlimited cloud storage (within fair use); the Lifetime plan allows 50. See Free vs. Pro.
I can't publish another design
That is a different limit from the cloud-design cap. Your plan includes a number of community publications, and the publish dialog shows how many you have used. Unpublish one to free a slot, or upgrade. Designs you have already published stay online either way. See Publish a design.
"Cloud is not configured (missing env vars)"
This build of Boldbobbin was started without cloud settings, so cloud features are off. The editor and local saving still work. See Sign-in problems.
The save just failed
Check your connection and try again. If it keeps failing, use Save to this computer (.vemb)… so you don't lose work, then report it via Help → Report a bug….