To avoid this, click on create short link button, paste the actual link and then select the option only generate shortcode, without domain name in the URL as shown in the screenshot below
Click on create a short link, a code will appear as shown in the screenshot below, copy this code and add it to the Button link placeholder. This code will have the actual link that is https://abc.com/xyz
Now save the draft and do a "Send Test", the actual message that you will receive will contain the button with the actual link.