فكان المهر مقدراً شرعاً
Thus mahr was treated as having a legally specified amount.
In Hanafi law the minimum mahr is stated as ten dirhams. This conclusion is not simply the dictionary meaning of faradnā; it depends on accompanying reports and jurisprudential argument.
Case 1: at least ten dirhams is stipulated.
Case 2: less than ten is stipulated. Under the Hanafi position, legal rules concerning the minimum apply rather than treating the smaller stipulated sum as the final amount.
The minimum of mahr and the validity of the marriage are distinct questions. A low stipulated amount does not by itself mean the marriage is automatically void.