Payment milestones have to be invoiced when reaching the achievements related to the specific milestones and as defined in the Milestone Payment Plan included in the contract. Each payment milestone is broken down to the amounts that pertain to each member of the Project team. Project Team members have to issue a specific invoice for the part of their competence. Subcontractors have to submit their invoices to the Prime contractor. The Prime contractor approves the invoices and submits them to ESA as specified in the contract.