Client apps key
This is key is required for working with the Yandex.Checkout libraries (right now, there's only one of them—mobile SDK).
You can get your key in your Merchant Profile in the Store settings section. If you run several stores, each one will require a separate key.
The button for issuing the key is disabled by default. You can enable it by making a request to your Yandex.Checkout manager.
The key works just like the secret key: copy it, save it in a safe place, and activate it with a text message password.