Supposing that the Contract is ECC Option B and a group of BOQ items is for supply of material. The Contractor should only submit an application for payment on these items once the work is done, i.e. they have been delivered. However, as verbally agreed with the PM and to assist the Contractor with cashflow, the Contractor submitted an application for payment for these on the date of him ordering the material and this was assessed and paid by the PM.
Can the PM change his mind a few months / years later and decide that the material payment certificate was wrongly assessed (using 50.5) and then backcharge the Contractor interest for the upfront payment on the materials?