26/08/2026
Building an app inside someone else's platform is like extending a house you don't own. The foundations come free, but you can't move a supporting wall.
We put Agency Express's SignMaster board management directly inside Reapit, so estate agents can order, change and collect For Sale and To Let boards without ever leaving their CRM. A React app on Reapit Elements, a .NET service listening for property events, and boards that quietly keep up as a property moves along.
The wiring wasn't the hard part. The lessons were:
→ Treat platform webhooks as at-least-once and out-of-order. Recompute state, don't replay instructions. → Sales was tidy. Lettings led a double life: one status carrying both tenancy stage and marketing availability. An already-tenanted property has no journey to follow at all. → When automation and a real person reach for the same board, decide on day one who wins. (We let the human win.) → Half the rollout wasn't code. It was formalising the process with the agencies who actually use the boards.
Craig, our Lead Programmer, has written up the honest version: the architecture, the code we're proud of, and the parts that made us earn it.
https://accentdesign.co.uk/articles/building-apps-that-live-inside-someone-elses-software