How to convert free users to paid users? (I will not promote)

I have a startup that has attracted about 150 free users in 30 days. They use all the free services, log in weekly, search, export data, and connect their mcp adaptors. So they clearly like the service. But rather than paying, they just stop using it and wait out the rest of the month. How do you manage to get people to pay? Emailing them when limits run low? Discounts? Coupons? Part of me really just wants to call them and ASK them what they would pay for. But I don't really have a personal relationship wi