How do I change a customer's subscription frequency?

See core principles first

Using the Interface

It's very easy to use the web interface to add new subscriptions with your preferred logic.

Add a new payment with a recurring event either in production or your sandbox account.

Simply select how you want your subscription to end (if at all). See images below to set up subscription correctly.

1. Go to Payments > Subscriptions
2. Find desired Subscription
3. Click on it
4. Click Edit 
5. Update Subscription details
6. Click Update

Using the API 

Steps: 

1. A simple POST /v1/subscriptions/{_id} with the specific subscription_id parameter

    "schedule":{
              "interval":"month",
              "start_date":"2018-08-01",
              "frequency": 3 // every 3 intervals
              "end_transactions": 4 // end after 4 intervals
         }

The API will accept data on only one of the end parameters. For example: