What you are seeing
You messaged the seller on an order and heard nothing back.
Why it happens
Most eBuy sellers are individual collectors, not shops with staff. They may be at work, travelling, or at a coin fair. Silence for a day or two is usually ordinary rather than a warning sign.
How to fix it
Give it two working days from your message.
Check the order status. If it has moved to Shipped, they were probably busy posting it and your question has answered itself.
Still nothing and an order is affected? Raise a support ticket from that order page.
Do not go looking for the seller on WhatsApp, Instagram, or by phone. A conversation outside eBuy cannot be reviewed if the order later goes wrong, and it is exactly the move scammers use.
How long it should take
Most sellers reply within a day or two. Support does not need the seller to reply before helping you, so an unanswered message is not a dead end.
If it is still not resolved
Raise the ticket from the order. Support can already see your messages, so there is no need to repeat the history. A seller who repeatedly does not respond to orders is dealt with separately from your case.