Hi Axel,
Keeping a conversation up and interesting on a dating site often requires that you ask something that intrigues the person. Use the person’s dating profile for ideas. Ask them a question related to something they described in their dating profile in great detail.
This is often what sets the spark and as you both chat, more and more highly effective follow-up questions can be created from that initial topic. This is often how you keep a person interested so that your conversations last a lot longer than what you have become accustomed to.