The REST module contains a reference to core HAL module and that is no longer in core.
Installing supporting modules
In order to use REST on a website, you need to install modules that provide serialization and authentication services. You can use the Core module HAL for serialization and HTTP Basic Authentication for authentication, or install a contributed or custom module.
Change help text in rest.module to the following,
Installing supporting modules
In order to use REST on a website, you need to install modules that provide serialization and authentication services. You can use the Core module SERIALIZATION for serialization and HTTP Basic Authentication for authentication, or install a contributed or custom module.
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Update The Patch For 10.1 And Addressed Comment #13.
Closing as duplicate of 📌 Remove last(?) references to removed extensions Closed: outdated