To test your Product Request link for your store, you'll need an IG account that has at least 5,000 followers to sign in. If you don't, you can whitelist an account with under 5,000 by manually adding the account to your Carro dashboard. Check out this article for instructions on how to manually add a profile to your Carro dashboard: https://support.getcarro.com/en/articles/2950177-manually-import-influencers-to-your-carro-dashboard
Once you have an account that you can sign in with, you'll be able to complete the Product Request flow. Just click on your Product Request link and follow the steps presented by Carro!