X_ADMIN_ACTION_DUPLICATE
Means
two registered admin actions carry one name
Typical cause
the same action name declared on two entities, or on an entity and the global toolbar. Refused at defineAdmin, not at the first call: the name is the MCP tool name, the default label key and the key callAdminTool resolves a handler by, so a collision is a call that succeeds against the wrong action and reports nothing
Fix
rename one in defineAdmin's actions — name: '<entity>.<action>' — so the bare name belongs to one of them; the cause names both holders