E mail it
Curiously many of the businesses that advertise with me do not have the facility.
Since most are local one man businesses who deal in cash it will be cheaper to deliver the invoices myself despite fuel costs.
I offer a discount for annual payment (in advance) which will help.
My U3A organisation asked a few months ago if we would be happy to receive the monthly magazine by e-mail. I agreed and have received said publication electronically. I have also still received it in the post. I've told them.
Those with a "National" payment system (WeightWatchers, Spar, etc) like to pay by BACS transfer but still post me a confirmation that they have made their payments.