"Instead of paying invoices by email." - it’s not clear what you mean.
How can I pay via WorldPay using email?
Maybe you just want to send invoices to customers when they make a purchase through an e-commerce? 
Or just create invoices to clients manually and send them to clients by email?
If so, then this is a built-in functional odoo independent of the payment method.
Look this video Sales Basics and Your First Quotation | Odoo Sales