How to find out the date of the next payment for a Paypal subscription?

Question

API

The Paypal subscription was created by the form:

<form id="paypalform" action="https://www.paypal.com/" method="post">
  <input type="hidden" name="cmd" value="_xclick-subscriptions">
  <input type="hidden" name="business" value="[email protected]">
  <input type="hidden" name="item_name" value="AAA">
  <input type="hidden" name="item_number" value="BBB">
  <input type="hidden" name="no_shipping" value="1">
  <input type="hidden" name="p3" value="1">
  <input type="hidden" name="t3" value="M">
  <input type="hidden" name="src" value="1">
  <input type="hidden" name="sra" value="1">
  <input type="hidden" name="no_note" value="1">
  <input type="hidden" name="rm" value="2">
  <input type="hidden" name="modify" value="0">
  <input type="hidden" name="currency_code" value="USD">
  <input type="hidden" name="return" value="https://mywebsite.com/paypal_ok">
  <input type="hidden" name="custom" value="20">
<input type="hidden" name="a3" value="50.00">
</form>

How can I find out the date of the next payment later?
Tried via API call:

https://api.paypal.com/v1/billing/subscriptions/I-ABCD12345'

but in the answer

{
    "details": [
        {
            "issue": "INVALID_RESOURCE_ID", 
            "description": "Requested resource ID was not found."
        }
    ], 
    "message": "The specified resource does not exist.", 
    "name": "RESOURCE_NOT_FOUND", 
    "links": [
        {
            "href": "https://developer.paypal.com/docs/api/v1/billing/subscriptions#RESOURCE_NOT_FOUND", 
            "method": "GET", 
            "rel": "information_link"
        }
    ], 
    "debug_id": "**********"
}