Amount of Mahr fixed After wedding . Valid marriage?

Salam aleykum, I hope you are well. I had my religious marriage (after a civil marriage) with the imam of a mosque. My guardian and my two Muslim witnesses were there. The imam asked us if we had agreed on the dowry; we didn't know how to answer because my husband and I hadn't set an amount, but the imam continued with the ceremony. The day before the wedding my husband asked me how much I wanted as a dowry, I told him we'd see on the day of the wedding but we didn't. Personally, I'm planning to ask for a dowry in the future. Personally, I intend to ask for a simple dowry (according to his means) but my husband doesn't know (we haven't discussed it). My question: Is the marriage valid even if we had no idea of the amount of the dowry while the imam was marrying us? WE will fix ( me and my husband) the amount later. Thank you for your help. Salam aleykum