Tweet Photo is the easiest way to tweet your Instagram photos.
Just connect your Instagram and Twitter accounts, and we'll take it from there. Tweet Photo embeds the photos in such a way that they show up on Twitter, unlike the native Instagram functionality.
It's free and only takes seconds to set up. Give it a try!
The built-in toggle on Instagram only posts a mangled version of your IG post to Twitter; it's just a link, the card functionality is broken, and even back when it did work it only "kinda" worked (didn't show multiple images, for example). You can do some of this with IFTTT, but it's more fiddly to set up and doesn't support multiple images.