As shown in https://docs.imember360.com/webhooks/i4w_date

The basic HTTP post only adds time to whatever the current date is and stores it in the target field. For example, the post below will add 2 weeks to today’s date, and store it in the custom field Next Meeting.

https://yoursite.com/?i4w_date=YOUR_SECURITY_KEY&target=_nextmeeting&operation=plus%202%20weeks

If you want to add time to whatever date is already stored in a custom field you have to use the “source” parameter, in addition to the “target” parameter. The post below would take the date in the field Last Meeting, add 30 days, and store that value in the field Next Meeting.

https://yoursite.com/?i4w_date=YOUR_SECURITY_KEY&source=_lastmeeting&target=_nextmeeting&operation=plus%2030%20days&format=Y-m-d%20H:i:s

An example for one of our sites is below:

https://loyaltyacademy.org/?i4w_date=40f729&source=_CLMPOnDemandExpirationDate&target=_CLMPOnDemandExpirationDate&operation=plus%2012%20month&format=Y-m-d%20H:i:s&Id=81467

This post takes whatever the date is in the field CLMP On Demand Expiration Date, adds 12 months, then stores that in the same field CLMP On Demand Expiration Date.

Without the “source=_CLMPOnDemandExpirationDate” included in the string, the post would only add 12 months to today’s date and store that in the CLMP On Demand Expiration date field.