Recharge Gift Subscription Parameters

I have a client using Recharge for subscriptions that wishes to offer gift subscriptions to a custom built web application. The two necessary functions are: 1) for the subscription to be flagged as a gift (and all that implies, e.g. receiver’s name and email), 2) a limit / end date of the subscription (e.g. 1x per week for 3 months, so, 12 deliveries).

Unfortunately, I cannot find documentation on the Recharge parameters needed to flag the subscription as a gift, and their support says a custom app is out of scope for support (they only provided me with gift widget documentation, which does not seem to work without the widget, which I do not want). I have tested the following parameters ChatGPT recommended, but they do not seem to work either:

data = {
​    "id": ​1​234567890,     
​    "quantity": ​1,
​    "selling_plan": ​2​345678901,
​    properties: {
​        is_gift: true,
​        gift_recipient_email: 'test@example.com',
​        gift_recipient_first_name: 'test1',
​        gift_recipient_last_name: 'test2',
​        shipping_interval_unit_type: ​'​weeks',
​        shipping_interval_frequency: ​1,
​        charge_interval_frequency: ​1,
​        subscription_length: ​12
​    }
}

If anyone has experience or is aware of documentation on this matter, I would greatly appreciate the help. Thank you!