How to connect the front end and back end server

am updating all the integration third parties then how i connect the server and front end shop owner,admin and end user app

I have updated the tutorial … plz see the tutorial here :
https://developer.nearbyshops.org/installation/installation-on-digital-ocean.html

You can connect your instance to end-user app and shop-owner app in multi-market mode and single market mode …

For Multi-market mode … ( i have done it already for you)
For Single-market mode … see this tutorial …https://developer.nearbyshops.org/installation/customize-apps.html