Custom code works on all paid plans (except for the archived Creator plan). With a Free plan, you can see working code in Preview mode but not in a published project.
You can connect Meta Pixel to your project by inserting the associated code directly into the <HEAD> section of the code editor.
The base Pixel’s code contains the Pixel ID twice. Make sure to copy the entire code snippet. Then go to your Readymag project settings, open the Code tab, choose the Code Editor and paste the code into the <HEAD> section.
Press “Save&Close” to apply changes, and then republish your project. You can find more details about getting started with Meta Pixel in this article.