Subscription variations through API

* Subject
Changing variation line-items via zapier or webhooks: Nothing changes

* Website URL:
https://dev.triggre.com/

* What are you trying to do?
We use variations for subscriptions. And we use Zapier, the Woocommerce zap and/or the webhooks to retrieve and change variations and subscriptions of our customers.

What steps did I take:
We can change these on two sides:
1. the user changes the variation himself by clicking Upgrade/downgrade in his portal.
2. we change the variation from our own back-end application and send that new variation to Woocommerce

Option 1 works perfect!
Option 2 is causing us some headaches.

What happens:
When I use the zap to update a subscription the new variation is being added to the current subscription. This results into two variations on the same subscription.

What would I like to see happening:
My intended result is to switch the variation, from variation X to variation Y. The intended result is that the customer will still only have one variation linked to his subscription and not an additional variation.

What am I sending via Zapier:
I’m using specific (‘hard-coded’) values to be absolutely certain i send the values I expect.

Function: Update subscription
— properties —
ID: 11368
Status: Switched

Line Items
Product Id: 11013
Variation Id: 11018
Quantity: 1

The page I need help with: [log in to see the link]