I asked my b2b customer for a 15-min check-in call. How should I run it?

I built a B2B SaaS and have a customer that has been using it for 4 months. They max out their usage every month, and I beat their incumbent head-to-head by 7x to land the deal. I asked for a 15 minute video chat to check-in.

I want to expand the number of seats they have with me.
I want to get referrals to companies they know that could use it.

How should I run this call?
Know of any customer success best practices / strategies?

Thanks