Hello! SkinsRestorer developer here. 😺
We have scheduled the release of the version 15.0.0 for the 28th of October after almost a full year of work on this new major release.
The API has been heavily modified and thus needs to be implemented for dynmap to support.
Moving forward the API contains a Version Provider class
Which you can use to load different implementations of our API based on for example the major version returned.
This class only exists starting v15+ and will be in every future version of SkinsRestorer, even after major releases.
Here are a few resources to help you implement the new API:

• Javadocs
• API Example
• Our website documentation (not very in-depth yet)

If you have any questions about the API, feel free to ask them here directly or in our discord server

[15:31:40] [Server thread/WARN]: [dynmap] You are using unsupported version of SkinsRestorer. Use v14.1 or newer.