Problem with Exporting App-Data to Drupal (Webhook?)

Hello,

Our team uses Podio and we want to export/display several data of podio apps on our former website which is based on a Drupal CMS. (For example to show which team members are member of particular sub-projects.)
I started testing with a small app only containing a simple text field.
Unfortunately, I don't succeed importing the podio table columns...
(I follow the first tutorial on http://artur-thiessen.de/blog/datenmigration-podio-zu-drupal#comment-5)

Here is my setup:
1) podio App "MyApp" containing items with each containing:
- a text field "Title" (with external ID and field ID)
- an Item ID "Item_123" (which I don't know how to access in Drupal by the way)
2) The App has an App ID and a token and activated webhooks for "www.xyz.com/import/MyImporter" (is there a difference between www.xyz.com and xyz.com? Our website works with both but what about the API Key?)
- item.create
- item.update
- item.delete
3) API Keys for the website (again, is there a difference between www.xyz.com and xyz.com?)
4) Drupal:
- Installed modules: Feeds, Feeds Podio Fetcher, Feeds JSONPath Parser, Podio Listener Module (and optional Feeds Tamper, Feeds Tamper PHP)
- Installed libraries: Podio PHP Client
5) Configuration of the drupal modules:
- the podio app data columns are bounded to a content type structure I created in podio, containing the fields "title" and "field_1_textfield"
- on www.xyz.com/import/MyImporter : Client ID, Client secret, Podio App ID, Podio App Token similar to the settings in podio
- JSONPath Parser Settings:
> Context: "."
> title: "fields.0titel.value"
> field_1_textfield: "fields.0titel.value"
6) Now comes the problem: When I try to start importing, on www.xyz.com/import/MyImporter , the import seems to begin and shortly after returns the following message:

"Ein AJAX-HTTP-Fehler ist aufgetreten HTTP-Rückgabe-Code: 500 Im Folgenden finden Sie Debugging-Informationen. Pfad: /batch?id=1041&op=do Statustext: Service unavailable (with message) Antworttext: Recoverable fatal error: Argument 2 passed to FeedsJSONPathParser::parse() must be an instance of FeedsFetcherResult, null given, called in /home/web1646/public_html/sites/all/modules/feeds/includes/FeedsSource.inc on line 354 and defined in FeedsJSONPathParser->parse() (Zeile 18 von /home/web1646/public_html/sites/all/modules/feeds_jsonpath_parser/FeedsJSONPathParser.inc)."

English:
"An AJAX-HTTP-Error occured HTTP-Return-Code: 500 Debugging-Information:
path: /batch?id=1041&op=do
status text: Service unavailable (with message)
response text: Recoverable fatal error: Argument 2 passed to FeedsJSONPathParser::parse() must be an instance of FeedsFetcherResult, null given, called in /home/web1646/public_html/sites/all/modules/feeds/includes/FeedsSource.inc on line 354 and defined in FeedsJSONPathParser->parse() (line 18 of /home/web1646/public_html/sites/all/modules/feeds_jsonpath_parser/FeedsJSONPathParser.inc)."

I think that no data was passed, so maybe there was a problem with the verification of the webhooks? (podio says, the webhooks are "inactive")
How can I verify the Webhooks or fix the problem in a different way?
Is there a way of passing the Podio App Data Columns to Drupal Views in order to show them in a table?

Thank you for your help!
Matthias

P.S.: Here is an overview of a configuration with a SINGLE Item Fetcher (I am using Multiple Item Fetcher of the Module "Feeds Podio Fetcher" because I want to import several columns and not a single one. The Names may differ but the error message is the same):
Basic Podio Drupal Configuration