Limit of inviting a guest outside an organization on a free plan

If we are trying to invite the guests outside the organization, it will become very difficult for us to keep a track and know once the limit of 100 invites outside the organization is reached as it does not show an error message for the same that the limit is already expired - rather gives a notification “invited <n> member to <ABC> Team and <XYZ> project” unless we check with the invited users if they have received an invitation and this will be a tough task to monitor as most of them lies outside the organization and there can be multiple to and fro for the same. Please advice.