Is the khulʿ valid if an agreement was reached on compensation at a later time and its amount was not specified, and then the husband refused the compensation offered by the wife?

According to the majority of scholars, khul' (divorce at the wife's instance) is valid even with an unspecified عوض (compensation). So, if a woman seeks khul' for an unspecified item, such as an unassigned slave, or for "what is in her hand," or with a فاسد (invalid) condition, the khul' is still effected, and she is obligated to pay مهر المثل (a dower equivalent to that given to women of her status). The khul' with an unspecified عوض is valid because it is the relinquishment of a right (إسقاط حق), not a transfer of ownership (لا تمليك). Relinquishment allows for leniency (المسامحة), and because khul' is permissible even without any compensation at all.