Is it obligatory for one who has contracted his marriage to a girl via video call, and saw her without a head covering, then differed with her and wishes to divorce her, to pay her dower?

If you divorce your wife before consummation or khalwa (definition) (private seclusion) with her, she is entitled to half of the agreed-upon mahr (dowry), unless one of you waives their right. If no mahr was specified, she is entitled to a mut'ah (consolatory gift) that is appropriate for your financial situation, the estimation of which is left to the judge in case of dispute. Seeing the wife through social media does not constitute khalwa that necessitates the full mahr.