When trying to delete a Split that exist in multiple Environments, The error below show up:
However, after deleting all the custom targeting rules, the error persist.
The error is referring to all the Split definitions within the environment, meaning, Treatments, Whitelists, Dynamic Configs and Default Rules in addition to the Custom Targeting Rules.
To delete all the definitions, click on the second (...) icon from the top right and click on Delete targeting rules option
Repeat the same action for all other Environments that the Split is added to. Then the delete Split option will work successfully