How to upload Instagram posts to Snapchat automatically
Here is how to upload Instagram posts to Snapchat, so that every time you post on Instagram, the post gets automatically posted on Snapchat (and any other social networks you select).
Using OneUp, you first connect your Instagram account and Snapchat account (and any other social network you want to autopost to):

Then choose “Cross-posting” from the Create A Post dropdown options:

Then choose Instagram as the “Post from” account, and choose Snapchat (and any other social network you want) as the “Post To” account:

That’s it! Now moving forward, whenever you post on Instagram, it will automatically post to your Snapchat account with 2 hours of the original post.
Or you can optionally choose to add a delay so that it doesnt post to Snapchat until after a few hours or days.
Here is a video showing how the autoposting process works in OneUp:
FAQ
Does this work with both image posts and video posts?
Yes, OneUp’s cross-posting works with both image and video posts, so that whenever you post an image or video post on Instagram, it will automatically post to your Snapchat account automatically.
If I add music to my Instagram video post, will that music also be added to the Snapchat post?
Yes, it will post the video with the music to Snapchat.
So this works even if I post to the Instagram account from the Instagram mobile app?
Yes, this works regardless of whether you post to Instagram from the Instagram mobile app, from instagram.com, or from a scheduling tool.
Does this work for autoposting from Instagram to multiple different Snapchat accounts at the same time?
Yes, OneUp’s crossposting feature allows you to autopost from Instagram to multiple Snapchat accounts at the same time.