We've been working hard to extend the reach of PWA developers; proud of what we've delivered on desktop and mobile this year!https://twitter.com/ChromiumDev/status/1126543605622026241 …
You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
E.g., Apple *still* hasn't implemented push notifications 
...but I use Twitter Lite PWA added to the home screen on iOS and it works great (modulo missing features), so PWAs are available there (but developers report many Safari bugs). Also, they're only installable from Safari.
iOS respects the manifest? Since when? Is that very recent?
11.3, I think.
Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.