Answer found

But it's only available in these languages:

• English (United States): Is it possible to buy additional monthly streaming minutes?
• Deutsch: Kann man zusätzliche monatliche Streamingminuten kaufen?
• Español: ¿Se pueden comprar más minutos mensuales adicionales de streaming?
• Français: Est-il possible d'acheter des minutes de streaming par mois supplémentaires ?
• Chinese (Sim.) (简体中文): 是否可以购买额外的每月流媒体时间？
• Português: É possível comprar minutos mensais adicionais de streaming?