This ticket affects the documentation for enabling headless-p13n on a custom bundle: https://docs.magnolia-cms.com/product-docs/6.2/Modules/List-of-modules/Personalization-module.html#_personalization 

To enable p13n-headless - one must add magnolia-personalization-rest to the bundle.
This has been a bit complicated so far, because:

• dx-core generally was using personalization v. 2.0.15
• but magnolia-personalization-rest exists only as 2.1.0
  In consequence people had to include dependency management for p13n 2.1.0 in their pom files.

It will become much easier in version 2.1.1
To enable headless-p13n - you only have to add magnolia-personalization-rest to the custom module.