How does an Admin or a Members Manager enter a monthly payment for a membership?

Look for the member in the Search Field at the top left of the website

Select the member for who you want to enter the membership payment

Go to the member tab

Scroll down to the bottom of the page and click on Set Up Monthly Payments

Scroll down and click on Subscribe With Credit Card

Enter your credit card information and click on the Pay button

If you go to the Member's tab and scroll down, you can see that "Your Monthly Payments" are active.