If you want to use 2Checkout Payment Gateway for the site, you need to read this article.
Setup Regular Price
2Checkout currently supports recurrence intervals that will allow the sale to bill your customer every week, month or year.
If you want to create a plan, let’s say, 20$ per week, you have to enter exactly “7” in Regular Period day field.
Similar to monthly, it should be 30 in Regular Period and 365 means Yearly. You can’t enter a number, which is bigger than 365.
The trial Period setting is not available for 2checkout.
You can’t set up a plan with 20$/7(days), allowing 10$/3 first days.
But you CAN set up a plan with 20$/7(days), allowing 10$/7 for first billing (only).
It means if you enter a value in Regular Price field, the Regular Period day is Trial Period day.