Hello Odooers, 

We are running a management and consulting company in the field of software technology. Our business model is designed in a way that the software implementation of the projects is implemented by external suppliers as partners, and the payment terms are back-to-back between us, the customer, and the supplier. Meaning that if, for example, we agreed with the customer to receive a 40% downpayment and two other payment of 30% each during the project time, I do the same with the supplier after I receive the payments from the customer. 

Now, I want Odoo to restrict any vendor bills payments if the related customer didn't pay for that milestone yet and in this case, the system should have managerial approval first. Also, I want the system to check if the vendor bill for some milestone has the same percentage as from the client. If not, then it must have managerial approval also. 

How do I can implement this?

Thanks in advance