My company does architectural consulting and testing. I have a client that we sent a proposal to, they signed, then we performed the work. They were satisfied with the work. Then once the invoice was sent they said we had to go through their system to get payment, and their system including signing an additional lengthy contract that our owner did not want to sign. We explained this to them and they agreed to pay the invoice, but never did. Eventually we asked for payment again and now they say they are not going to pay the invoice. The invoice is around $6500 dollars, this was the first (and last obviously) work we've done for this client. They are a luxury apartment complex owner that has apartments nationwide. We sent the invoice 6/10/2019. The work was finished and report sent 5/14/2019. Looking to see what our options are or if this amount isn't worth the trouble. Thanks, B