To check campaign stats on via Leadeth Reports, look for the chart showing 'Invite to Events' - here you will see on the graph how many invites have been pushed daily for the period chosen. You can also filter by campaign if you have multiple event invitation campaigns running. Try to minimise any manual inviting as this will lead to limitations be hit sooner.
P.S. In the Daily Limitation Settings within LEadeth, I'd max up the Invite to Events range from 120-150 per day.
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