At first you need to create a category to hold your data.(the category name will be hashed by the cryptographic algoritim assoiciated to your user and salted by a random salt stored on your account data).
when u have a category u can start storing out key - value hashes, they are stored also by using the crypto algorithm associated to your account.
the key is salted by using the salt for your account and the salt of its category
the value is salted by using the salt for your account and the salt of its category and its own salt.

making the api have near to zero knowledge over the values being stored,