Sandbox: Revise subscription returns success but subscription not modified?

[s4brown]

Hello,

I seem to be making a successful call to revise a subscription quantity, but the change is not reflected in the merchant account and subsequent calls to retrieve the subscription return the original quantity. For example, I have a subscription with a quantity of 3 and send this request:

Endpoint

https://api-m.sandbox.paypal.com/v1/billing/subscriptions/I-MWR9T4XRKFLU/revise

Body

{"quantity":2}

I am getting a 200 response code and the following response body

{"quantity":"2","plan_overridden":false,"links":["hateos links removed for clarity"]}

When I retrieve the subscription details or view the subscription in the merchant account  the quantity is still 3

Help!