Multi-vendors feature to ecommerce android app

Hi there, I have a grocery app, users orders. now i have multiple vendors , i need to add a screen so customer can select vendor of their own choice. technically app will be pointing to different back-ed admin portal. for example right now i have one and and one backend portal (php code) now next if customer select Vendor 1 then app will point it to backend admin portal url 1 Vendor 2 --> url 2 Vendor 3 --> url 3 single app will have point to hit on different base urls depend upon what customer will select. Note: customer should not place one order by selecting mix items from different vendors . Cart will be different if vendor change. [login to view URL] (need to add new screen like this) following is link of current app [login to view URL] Simply I need to run multiple different shops under one single app