A client going quiet mid-project is unsettling but usually not personal, most of the time it's a busy stretch, an internal shakeup, or a delayed decision on their end, not a signal that they've abandoned the project.
Start with a simple, low-pressure check-in rather than an anxious or accusatory message: a short note confirming where things stand and asking if anything has changed on their end. Give it a reasonable window, a week or two, before escalating further.
If silence continues, send a written summary of where the project stands, what's been delivered, what's outstanding, and what's needed from them to proceed, along with a clear timeline for how long you'll hold the work before pausing it. This protects you either way: if they come back, there's a clean record to restart from; if they don't, you have documentation for a kill fee or partial invoice.
If real money is at stake and enough time has passed, move to a formal collections letter sequence, and consider whether a dispute bundle is worth preparing in case it needs to go further.