When I click “Install” I get redirected to this broken link that shows a 404:
https://palantir.com/workspace/now/platform/4c112433-28d0-47f3-9600-531d84ff2a33?install=true
in the top right on build.palantir.com, you should see the enrollment url you have set, presumably palantir.com by your comment on where the link landed.
Click on that and please set this to the enrollment url you wish to open (it should look like example.palantirfoundy.com) if there is already a foundry account you have access to, or sign up for AIP developer tier for free to create your own foundry instance.