In order to publish lead ads on Facebook or Instagram, you will need to accept Facebook's Terms of Service. Here's how to do so.
Go to Facebook
You can find the Lead Ad Terms of Service page here.
Choose Your Page
In the upper left, you should see a dropdown menu with all Pages connected to your account. Make sure the Page linked to your SendGrid Ads account is selected, then click "Accept".
In the example below, I'm choosing my Facebook Page "loader.io". Your choices will be different.
You should see a success message once it's complete.
Once you see this, you can navigate back to SendGrid Ads and complete your campaign.