If you can't fulfill your deliverables within the timeline you promised, you can ask the buyer for an extension. They're not obligated to grant it, and they can ask for a refund.
Avoiding it in the first place
The single best way to stay on top of your projects: keep an eye on the notification box that shows up at the top of your dashboard. Any project with new activity (a buyer message, a status update request, anything that needs your attention) lands in a purple alert box up there.
If a project has the "Please provide a status update" tag, that's a buyer asking specifically for an update because they haven't heard from you in a while. Get back to them quickly to keep the project on track.
If you do need an extension
Message the buyer directly on the project page and explain. Most buyers are reasonable if you give them advance notice. If they decline and want to cancel, they can request a refund and we'll work with both sides on a fair outcome (see the "What if we have a disagreement?" article).