When you activate a renewal, it becomes an active contract and billing schedules are created from the contract start date up to today plus the number of months specified in the Billing Schedule Number of Months field in the Billing Central Settings custom setting. See Billing Schedule Number of Months.
To activate a renewal:
Click Activate on the Billing Contract Detail page of the renewal that you want to activate.
If a popup appears indicating there are incomplete contract lines, click Edit Contract, complete the contract lines then try again.