Sync your Stripe account to you Postgres database.
https://supabase.com/ is a good alternative, but I don't know if the data is hosted in Europe.
Secure Backend Server for Web, Mobile & Flutter Developers 🚀 AKA the 100% open-source Firebase alternative.
You can look into using appwrite.io which is an open-source (and self-hosted) alternative to Firebase. But you will need to host it somewhere on a cloud service AWS/DigitalOcean/etc
Build time-series-based applications quickly and at scale.. InfluxDB is the Time Series Data Platform where developers build real-time applications for analytics, IoT and cloud-native services in less time with less code.
Parse Server for Node.js / Express
Or maybe Parse (https://parseplatform.org/), the somewhat forgotten OG of PaaS.
Announcing Appwrite 1.0
5 projects | reddit.com/r/selfhosted | 14 Sep 2022
Parse Server or AppWrite
3 projects | reddit.com/r/FlutterDev | 8 Aug 2022
Migrate Firebase Users to Appwrite
2 projects | dev.to | 14 Sep 2022
Backend (auth/payment) options for Flutter app and web.
5 projects | reddit.com/r/FlutterDev | 20 Aug 2022
3 projects | reddit.com/r/iOSProgramming | 15 Jul 2022