What is the obligation regarding the dower (Mahr) when the agreed-upon dower is invalid due to lack of Sharia authorization?

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The entire dower obligation falls upon the husband because specifying the dower in this situation is invalid, as it was not sanctioned by Sharia. Therefore, the husband must provide the dower of the like (Mahr al-Mithl), similar to the case where he marries her based on a prohibited relationship (Muharram). The guardian (Wali) is liable for guaranteeing this amount because he was negligent in his duty, just as if he sold her property for less than its proper price. Imam Ahmad expressed apprehension that the guardian might be held liable.