Hi @tadeaspetak, your tags look fine. The card is also rendering fine. You also included the twitter:site parameter which enables card analytics.
This is a bit out of scope of this forum, but your Tweets may not be getting the amount of exposure you need. Besides using different social strategies to help you gain more followers and engagement I would suggest the “App Install Card” you can create at ads.twitter.com. This will allow you to promote your Tweet to your core audience. Within the ads.twitter.com dashboard there are other avenues to get assistance/help.
If it make sense for your use case, you can also integrate Fabric into your app so your users can share deep linked content from the app. Users may be more willing to engage with Tweets from their friends. Hit the Fabric forum or Fabric.io for details.