PHP API issue with 'Create a Custom Recurring Payment


i’ve API issue ‘Create a Custom Recurring Payment’ im using this method: xml-rpc - Keap Developer Portal (using PHP not PHP iSDK)
when i use ‘numberOfPayments’ 9999 the API gives error “The numPmts must not exceed 999” but creates the Subscription in IS backend with payment plan 2018-11-28_1308, when i use ‘numberOfPayments’ 999 api do not gives any error with response ‘1’ but the payment plan does not shows in subscription which causes missing of product from fulfillment report?

My concern is that why payment plan is created when API gave error and not when API give no error?