Why does my menu link not show a picture preview on WhatsApp?

WhatsApp builds the preview from tags in the page's head: title, description, url and an image. If the page lacks them, or the picture is too big, no preview shows. WhatsApp says a preview is never guaranteed.

• Tags: the page needs og:title, og:description, og:url and og:image in its head, and none may be empty.
• Position: the head must sit within the first 300KB of the page.
• Picture: under 600KB, at least 300px wide, and not more than 4 times wider than tall.
• Test: type the link in a chat without sending. If no preview appears after 10 seconds, check the points above.
• No promise: WhatsApp makes a best attempt only, so also say in words what the link is.