Through the site settings

Chat for a Tilda website

In Tilda the widget code goes into the site settings — you do not have to edit pages one by one.

Where to paste the code

1 Get the code in the dashboard Connect the site in WidgetChat and copy the install line.
2 Open the site settings in Tilda Site settings → the More section → the field for HTML code inserted before the closing body tag.
3 Paste the line and save The code is added once and works on every page of the site.
4 Publish the pages again Tilda applies settings changes only after publishing. No publish, no chat on the site.

Adding your own code is available on Tilda's paid plans. The free plan has no code field.

Look at the published site — The widget does not run inside the Tilda editor — open the real address.
Check the domain — If the site opens both on the Tilda domain and on your own, put the address people actually visit into the dashboard.
Write to yourself — Send a message from the chat and make sure a topic appeared in the Telegram group.

For third-party code, yes: the code field is available on paid plans.

Usually the pages were not published again after the settings change, or the site address in the dashboard does not match the real one.

No, the widget does not run in editing mode. Check it on the published site.