How Do You Price Per API Call?

Most of the 90 million eip monthlyapi calls come from payment gateways or your tone. You have 200 direct customers, and you reach another forty 500 or forty 800 through partners. How do you price for this? I mean, obviously per API hit sort of pricing is very popular these days. But how do you do it? It's between four to eight cents. And has it always been that way? R of your moving sort of up or down market?