As a CSA Coordinator for several years, I have worked with my City Attorney's Office to ensure that there is verbiage in each of our vendor agreements that each contracted vendor must agree to regarding when they must have all purchase orders, invoices, and supporting documents submitted to my office for payment prior to the close of the fiscal year.  My fiscal staff make calls, send out emails, and letters throughout the year to keep vendors from falling behind with billing.  Lastly, my team sends letters to each contracted vendor whether there is an outstanding invoice or not, reminding them that all purchase orders, invoices and supporting documents as outlined in their vendor agreement are due no later than July 31st.  If these documents are not received, the letter explains that the vendor is forfeiting payment due to noncompliance with contractual obligations.  This process is supported by our localities policies and procedures.