Do I have grounds to sue for a late payment on professional services if my client executed a poorly written agreement with their end client?

I run a business that provides land-use planning technical reports. I have an invoice to a client that is nearly 9 months past due. My report was incorporated into a larger report that the client submitted to a municipal government (let's say, 'city'). My subconsultant agreement has the standard language that the client would pay me within 10 days of their getting paid by the city. However, as I've found out, my client executed an agreement with the city that stated that the city would not have to pay the client until all of the technical reports had been reviewed and accepted by the regulatory agencies (which often takes months and months). These payment terms are highly unusual and I would never agree to them if I were the client. Do I have grounds to sue the client because their prime contract, unbeknownst to me, had unreasonable payment terms? I of course was unaware of the terms until just recently, since the prime contract was confidential.