Delay due to advance payment

Hi All ,

I'm working on a project started on 22-Mar-20 , as per the agreed contract ; an advance payment must be paid by the client at the begining of the project .

until now the payment still not processed , the contractor is facing a lot of delay due to delay in placing order for the materials to vendors , in this condition the programme is delayed about 3 months.

how can I build a claim regarding this matter ? 

Thanks ,

I really appreciate all your support regarding this matter.