Trading unpaid invoices for provided services in the UAE

We have been working for a Dubai based company since 2007.

Over the years we have sent many invoices and the company has paid the invoices, a lot of times too late but paid. We kept on doing services for this company since we had a good private relationship.

The debts kept building up and are today 1.5 million USD. The company signed an "Acknowledgement of Debt Agreement" and accepted that they owe us the money.

The company's CPA sent us several Balance Confirmation letters and asked us to confirm the debts. We signed and returned. They have not paid anything since 2015.

We do have some signed invoices, signed order of confirmations in regards to the service we supplied and many emails that confirm that we discussed the debts.

We think we have a strong case but we consider to sell the claim. Is it legal to trade claims in the UAE? How do you see our case?