Generate a unique number for every item sold

Hello, just joined this forum and looking forward to learning from its members. I currently am seeking any advice on how to generate an automatic code number for each unique sale made on my soon to be launched site. I will be selling services on behalf of other parties and need to confirm when service is delivered in order to remit payment. Any ideas how this is done? I am using shopify and PayPal but can't find a solution there. I would be very grateful for any kind of assistance you could…
Generate a unique number for every item sold

See original post by rickjacksonqld