[TYPO3-dev] Composer installation add TYPO3 extension

[Philipp Wrann]

Hey, again - composer installation not working for me

I added 
{
	"type": "composer",
	"url": "https://composer.typo3.org/"
}

to my repositories

Then i used:
cmposer require causal/image_autoresize dev-master

Extension is loaded correctly

When i enter the extensionmanager and press "activate" - i mean i HAVE to do that, right? - i get this exception:
#1245673367: The given class "Causal\ImageAutoresize\Slots\ExtensionManager" is not a registered object.
https://wiki.typo3.org/Exception/CMS/1245673367

I used this resource:
https://composer.typo3.org/

TYPO3 version is 7.4

Am i simply to stupid to use composer and typo3?