Hi,
To record the transaction where in the customer is purchasing the material from vendor, the suitable option is the Downpayment Invoice which records for the transaction and the advance payment which needs to be made. The downpayment document can finally be applied and closed with a final invoice in the system when the goods are received from the vendor after processing.
Have you tested the Downpayment scenario in the DEMO and checked with the client on its working?
Regards,
Jitin
SAP Business One Forum Team