Facebook and Instagram do not allow you to require likes, sharing, tagging, etc in exchange for entries. This excerpt is from their terms:
You must not incentivize people to use social plugins or to like a Page. This includes offering rewards, or gating apps or app content based on whether or not a person has liked a Page. It remains acceptable to incentivize people to login to your app, checkin at a place or enter a promotion on your app’s Page.
To ensure quality connections and help businesses reach the people who matter to them, we want people to like Pages because they want to connect and hear from the business, not because of artificial incentives. We believe this update will benefit people and advertisers alike.
Based on tis policy, this is why our Facebook Visit Page action has Likes marked as optional. Towever, we do provide Like and Share Actions you may use at your own risk.
Note: You can use the Refer A Friend action to have people share your giveaway on Facebook. The entries are given when someone refers another person to the giveaway but not when it is shared to work around the Facebook Rules.