Where the button actually appears
Telegram gives every bot one menu button beside the message box. By default it says Menu and lists commands. Once your shop is on, that button opens the storefront instead, which is the shortest path a buyer can take: one tap from the conversation to your catalogue.
This matters more than it sounds. Most people who want to buy from you will not scroll back through a chat looking for a link somebody posted in March.
Turning it on
In the dashboard, open the bot you use for selling and switch the product catalogue on. The shop button is set for you at the same time, pointing at your storefront. Nothing needs to be typed into BotFather and nothing needs deploying.
If you connected the bot a while ago and the button still says Menu, reopen the chat. Telegram caches the old button for a short time on the client side.
Check it the way a buyer sees it
Open the bot from a different account, ideally on a phone rather than desktop. Tap the button. You should land on your catalogue with your products, your colours and your shop name. If you see an empty shop, the products are probably still drafts rather than published.
Give it a second entry point
The button is the main door, not the only one. Pin a short message in your channel with the same link, and put the link in the bot description so a new subscriber sees it before they have said anything. Two entry points cover the people who never look at the menu bar.
What to check after the first day
Watch where orders stop. If people open the shop and leave on the first screen, the problem is usually the first row of products rather than the button. Move your best-selling item to the top and see if the number changes.