How to apply App Platform Static Site Catchall to Custom Domain

I have a static site SPA (Vue.js and Vue Router) running on App Platform. I specified a domain managed by DigitalOcean (in addition to the default ingress) in the App Spec. My App Spec has a catchall of ‘index.html’ to allow the SPA to behave correctly as routing is performed on the client side. When requesting any route from the default ingress ‘[application-uuid].ondigitalocean.app’ the webpage/routing works as expected. However, when I view the webpage from the configured domain, only the ‘/’ route works. All other routes return a default 404 page from DigitalOcean. It seems that the catchall isn’t working for my configured domain. How do I modify the App Spec so routing behaves similar to the default ingress when requested using the configured domain?