# X_ERROR_UNDECLARED

## Means

a handler threw a 4xx code its errors: list does not declare

## Typical cause

an action or query declares errors: and its handler threw a refusal outside that list, in a test or development run or in the contract scan of the handler source

## Fix

`add '<CODE>' to errors: in the declaration the cause names, or stop throwing it there, then: x verify --only contract`

[Core and runtime](/error-codes#core-and-runtime)