Complete Invoicing CRUD functionality

We have a finished developing the front-end UI of our Invoicing WinForms form. We would like a backed developer to finish the Save, Edit, Delete, Print, Send fuctionality of the Invoicing form. We need a unique invoice number for each new invoice and the ability to select which number we start from next invoice.

C#, Winforms, ,Net Framework 4.8, Devexpress Components for Winforms