When WhatsApp stops working

Most WhatsApp faults are one of about six things, and they are not equally likely. The single tick that never becomes two ticks is almost always the recipient's phone being off or offline — not a block, which is the conclusion most people jump to first.

Every troubleshooting article here is ordered by likelihood rather than by how technical the fix is, so the first thing you try is the thing that is most often wrong. That ordering matters: working through a list alphabetically wastes your time on rare causes.

Where a symptom has more than one plausible cause and no way to distinguish them from the outside — blocked versus phone-off is the classic — we say that plainly instead of pretending there is a reliable test.