When performing an upgrade to your subscription plan, Nelio Content prorates the use of your current subscription plan. That is, we refund what you didn’t use from your original subscription plan (based on the number of days remaining before renewal) and then immediately charge you for the remaining days of the new plan. The returned invoice on the Billing History corresponds to this prorated amount.
Nelio Content’s subscription are managed by FastSpring. If you want to know more about this topic, please read FastSpring’s explanation on how prorating works.