Include tier attributes in request body

[joannasese]

Reported issue: When using the subscription_update call, a plan with tiered pricing will fail, with an error requesting additional parameters not specified in API Request.

Expected result: Subscription should update, regardless of tiered add-on state.

Actual result: Subscription will fail to update, with errors around tiers, unit_amount_in_cents and tier_quantity.

Sample xml:

<subscription>
  <timeframe>now</timeframe>
  <subscription_add_ons>
    <subscription_add_on>
      <add_on_code>muppy</add_on_code>
      <quantity>3</quantity>
      <revenue_schedule_type>evenly</revenue_schedule_type>
      <tier_type>tiered</tier_type>
      <tiers>
        <tier></tier>
        <tier></tier>
      </tiers>
    </subscription_add_on>
  </subscription_add_ons>
  <collection_method>automatic</collection_method>
  <custom_fields></custom_fields>
</subscription>

Solution:
Include tier attributes in request body. This also activates PUT /v2/subscriptions/:subscription_id

Sample xml:

<subscription>
  <timeframe>now</timeframe>
  <subscription_add_ons>
    <subscription_add_on>
      <add_on_code>muppy</add_on_code>
      <quantity>3</quantity>
      <revenue_schedule_type>evenly</revenue_schedule_type>
      <tier_type>tiered</tier_type>
      <tiers>
        <tier>
          <unit_amount_in_cents>400</unit_amount_in_cents> 
          <ending_quantity>800</ending_quantity>
        </tier>
        <tier>
          <unit_amount_in_cents>200</unit_amount_in_cents>
          <ending_quantity>999999999</ending_quantity>
        </tier>
      </tiers>
    </subscription_add_on>
  </subscription_add_ons>
  <collection_method>automatic</collection_method>
  <custom_fields></custom_fields>
</subscription>

[bhelx]

Let's add a comment here for context.