Find the list of reasons why contract not processed during the period processing (TCODE: RERAPP):
1. Contract might be not activated - Check the System Status & User Status.
2. Real Estae Object might be not activated - Check the System Status & User Status.
3. Posting Parameters - tab shows the Frequency if you are running out of the frequency check this.
4. Term - tab Check the Contract start date & 1st Posting date
5. In the Terms tab of your contract , check field "Cash flow start date". Based on this date the system generates(plans) cash flow which gets posted by RERAPP.
6. In the RERAPP screen due date field by default shows <= symbol, means any cash flow planned before or on the date given should be posted. I would suggest to select a later "Due Date", for example "Contract End Date" and see if the syste generates any postings for futute period.
7. Authorization failure also an issue for not calling the contract.