Welcome to the forum m8.
Like @forkyeah said you need a clean entrance as well with clean path to accept purge.
But the mechanic of purge still needs work from both sides, players and devs. For example yesterday i started building a purge base. When i placed the foundations i placed a treasury too. It said that i can accept purge and i saw the camp to be created so i log out to stop it and log in to start building walls. Wnen i finished it i made 6 efforts but i took the message you get as well. So, you’re right, the purge trigger is a bit broken. But we need to learn a lot our self too.
Welcome again m8