I have some web/mobile apps and I'm currently using Adapty which has custom paywalls and other sorts of features, as well as web-based paywalls now that Apple lost their ruling against Epic Games (and I'm using Flutter but the UI side doesn't necessarily matter due to the web-based nature of the paywalls). Is this a use case you are targeting? Adapty also integrates with Stripe for the web side of its offerings.
Adapty looks cool! Kind of similar to Revenuecat?
I think the offering is similar -- both manage entitlements and paywalls. And while we do have a proportion of users that use us for mobile apps we're pretty focused on SaaS / web.
I can imagine Adapty would go deeper on features like AB testing, paywall designing etc
Our users handle lower volume of subscriptions but require more flexibility and depth on the pricing models they want to support.