Copy this URL and on the Datacake Rule, click the "Add Action" button. Choose the "Call a webhook" option and paste your URL into the URL field. You can remove the "Content-Type" header using the (x) button on the right.
The "Payload" is the message that will be sent, so you can clear it, type your own message and optionally insert placeholders, for example like this:
You can then click the "Try Webhook" button, which should send a message to your Telegram account.