We are aware users are unable to invite the bot. This has been caused by Discord's automatic spam-detection systems. We have reached out to Discord on instructions for getting this lifted. Further updates will be posted in our support server.
When creating a giveaway include a text below the prize telling the users that the giveaway is hosted / created by the user who made it so they know who is responsible for it. I have seen this being implemented on GiveawayBot so here it is in action.