Unable to create label, fatal error in logs

Hi there,

I have not been able to properly activate the plugin and create labels. All information in the Account and API settings is added, the EKP has been reviewed and the username and password work with the DHL portal.
However, any time I try to create a label for an order on the order detail page, I see an endless spinner and no label is created. If I try to bulk edit the orders in the overview and select “create label”, I’m getting a critical WordPress error. (If i go back in the browser, the critical error does not persist)

This is the error I see in the logs:
Uncaught Error: Object of class stdClass could not be converted to string in /hp/cz/ab/ud/www/BienenbudeWP/wp-content/plugins/dhl-for-woocommerce/includes/REST_API/Parcel_DE/Client.php:57 CONTEXT: {“error”:{“type”:1,”file”:”\/hp\/cz\/ab\/ud\/www\/BienenbudeWP\/wp-content\/plugins\/dhl-for-woocommerce\/includes\/REST_API\/Parcel_DE\/Client.php”,”line”:57},”backtrace”:[“”,”#0 \/hp\/cz\/ab\/ud\/www\/BienenbudeWP\/wp-content\/plugins\/dhl-for-woocommerce\/includes\/REST_API\/Parcel_DE\/Client.php(57): sprintf(‘Error creating …’, Object(stdClass))”,”#1 \/hp\/cz\/ab\/ud\/www\/BienenbudeWP\/wp-content\/plugins\/dhl-for-woocommerce\/includes\/pr-dhl-api\/class-pr-dhl-api-rest-parcel-de.php(147): PR\\DHL\\REST_API\\Parcel_DE\\Client->create_items(Array)”,”#2 \/hp\/cz\/ab\/ud\/www\/BienenbudeWP\/wp-content\/plugins\/dhl-for-woocommerce\/includes\/pr-dhl-api\/abstract-pr-dhl-api.php(37): PR_DHL_API_REST_Parcel_DE->get_dhl_label(Array)”,”#3 \/hp\/cz\/ab\/ud\/www\/BienenbudeWP\/wp-content\/plugins\/dhl-for-woocommerce\/includes\/pr-dhl-api\/class-pr-dhl-api-paket.php(63): PR_DHL_API->get_dhl_label(Array)”,”#4 \/hp\/cz\/ab\/ud\/www\/BienenbudeWP\/wp-content\/plugins\/dhl-for-woocommerce\/includes\/abstract-pr-dhl-wc-order.php(1151): PR_DHL_API_Paket->get_dhl_la”]}

Please let me know if there is any other info you need.

The page I need help with: [log in to see the link]