Delivery ticks (✓ and ✓✓)

On messages you send over WhatsApp, an indicator shows how far they got — just like the app:

• ✓ — sent: Meta accepted it;
• ✓✓ grey — delivered to the customer's device;
• ✓✓ coloured — read;
• not sent (in red) — Meta refused it. Hover to see why.

The most common cause of refusal is a closed 24-hour window.

Instagram and Messenger do not provide this level of detail yet — there the indicator stops at "sent".