Oracle Message PCC-02427 - Expression is not of the correct character string type

ERRORExpression is not of the correct character string type
CAUSEThe given host variable expression was not declared to be of the required character type. In this case, one of several possible character types would have been accepted. However, the host variable type did not match any of them.
ACTIONRedeclare the problematic host variable, using one of the permitted character types.