This response is based on the information provided.  We strongly suggest you discuss with your contracting team, business financial manager and/or legal department as appropriate. 

In the Department of the Air Force Manual (DAFMAN) 65-605V1 section 5.2, Budgeting and Funding for IT resources, the Air Force guidance calls out Software Sustainment/Maintenance which addresses the costs incurred in continuing operations and current services which I interpret as a "yearly subscription fee".  This would be considered an expense and thus Operations and Maintenance (O&M) would be used to fund the fee.  You need to verify that you have included this in the O&M Budget Exhibits. Also, verify this interpretation with the funds certifier.