Substack has disabled all options of adding custom HTML. It is not possible to add Linkz.ai script to Substack at the moment.
Substack is a tool to grow a paid newsletter. You can add code snippets (custom HTML) including Linkz.ai script to Substack via Google Tag Manager. Substack does not support adding custom HTML, hence Google Tag Manager workaround. Here is the flow:
Create a free Google Tag Manager Account or login into your existing one
Add Linkz.ai script to your Google Tag Manager
Add your Google Tag Manager id to your Substack settings
Google Tag Manager will load Linkz.ai script in your Substack posts and your visitors will see link previews in your posts.
Updated on: 26 / 01 / 2022