I have an IT business.
I send invoices to my clients via email, if they didn’t pay it then I
send them a letter where I charge them 60p paper bill charge.
So I want to know if the 60p is Ribbis?
To send a bill it costs me 49p and I add another 11p because of tercha etc.
Since the charges are not for the delay in payment but for costs of sending the bill, there is no problem of Ribbis.
It is advisable to inform the clients in advance of these charges, such as including a clause to this effect in the initial contract.