According to the documentation - as of version 1.4, an access token is no longer required to display a user's feed when supplying a client ID, but I still get this error.
initFeed = function () {
var feed = new Instafeed({
clientId: '###',
get: 'user',
userId: '###',
});
feed.run();
}
I am in Sandbox mode, but cannot submit requests as Instagram says this is not needed for a third party app to display my posts.

Hey @heaversm! Shortly after 1.4 was released, Instagram changed their API terms and introduced the Sandbox mode you're referencing.
To work inside sandbox mode, you'll need to issue yourself an access token using the client ID Instagram gives you.
Sorry for the out-of-date docs!
To work inside sandbox mode, you'll need to issue yourself an access token using the client ID Instagram gives you.
How do we do that?
@suture try https://rudrastyh.com/tools/access-token