critical error after configuration of pusher

Hi folks,

I just bought your collaboration plugin and am very enthusiastic on using it soon. I followed the instructions: Installation of the zip-file of the plugin, activating of the plugin was fine. I registered at pusher.com and genereted the app keys. When I entered the app keys in the plugin settings and saved them, I produced a critical error with the following details:

Fatal error: Uncaught Error: Call to undefined method GuzzleHttpUtils::chooseHandler() in /html/stage.cvh-design.de/wp-content/plugins/dplugins-collaboration/vendor/guzzlehttp/guzzle/src/functions.php:61 Stack trace: #0 /html/stage.cvh-design.de/wp-content/plugins/backwpup/vendor/guzzlehttp/guzzle/src/HandlerStack.php(42): GuzzleHttpchoose_handler() #1 /html/stage.cvh-design.de/wp-content/plugins/backwpup/vendor/guzzlehttp/guzzle/src/Client.php(65): GuzzleHttpHandlerStack::create() #2 /html/stage.cvh-design.de/wp-content/plugins/dplugins-collaboration/vendor/pusher/pusher-php-server/src/Pusher.php(69): GuzzleHttpClient->__construct() #3 /html/stage.cvh-design.de/wp-content/plugins/dplugins-collaboration/src/Collaboration.php(125): PusherPusher->__construct(‘9619de7cc391f5e…’, ‘50653b079b7b0f0…’, ‘1317460’, Array) #4 /html/stage.cvh-design.de/wp-includes/class-wp-hook.php(303): DpluginsCollaborationCollaboration->boot(”) #5 /html/stage.cvh-design.de/wp-includes/class-wp-hook.php(327): WP_Hook->apply_filters(NUL in /html/stage.cvh-design.de/wp-content/plugins/dplugins-collaboration/vendor/guzzlehttp/guzzle/src/functions.php on line 61

Please, can you help me on that issue?

Thanks, Catharina

Help on Facebook said: deactivate BackWPup. Then the error was gone, but it still does not work. I do not get the collaboration info in the bottom right corner. What else is missing to get it to work?