uncapable
/ˈʌnkæpəbəl/Definitions
1. adjective
Lacking the ability or power to do something; unable or incompetent.
“The new employee proved to be uncapable of handling the complex project.”
2. adjective
Not able to be opened or closed; e.g., a safety pin or a zipper that is stuck.
“The zipper on my jacket has become uncapable.”