CustomFields in Subscription Plans - API answer ignores custom fields

Hi,

i configured a custom field in the Zoho subscription web interface in the products section

name: Features

type: TextBoxMultiline

After that I extended an existing plan and filled out my textbox which occurred as it should in the webinterface

But when I query the Zoho subscription api (GET /plans?filter_by=PlanStatus.ACTIVE)

I get the list of all my plans as a list but without the custom fields map.

find one entry of the list here:

{"plan_code":"Medquat","name":"Medium,quaterly","billing_mode":"prepaid","description":"","status":"active","product_id":"1464976000000065054","tax_id":"","tax_name":"","tax_percentage":0,"tax_type":"","trial_period":0,"setup_fee":2000.00,"setup_fee_account_id":"","setup_fee_account_name":"","account_id":"1464976000000000388","account":"Verkäufe","recurring_price":499.00,"interval":3,"interval_unit":"months","billing_cycles":-1,"product_type":"none","show_in_widget":false,"store_description":"","store_markup_description":"","created_time":"2019-09-29T20:11:15+0200","created_time_formatted":"29 Sep 2019 08:11:15 PM","updated_time":"2019-09-29T20:11:15+0200","updated_time_formatted":"29 Sep 2019 08:11:15 PM","addons":[]}

can you give me a hint what is wrong

thx Martin