The point of displaying posts by tag is that it would return all Instagram posts (regardless of user who posted them) that were tagged with a particular hashtag. Even if I wanted to only show posts that were tagged from my account (which is a business account and linked btw), the widget gives me the option to show by username OR tag (which doesn’t work) but not both.
The only way I see this working right now is if I setup a separate Instagram account specifically for the website (event) and have someone dedicated to making Instagram posts about the event. What I really wanted was for all our guests to be able to build the feed through the use of a hashtag.