async getPrivateKey(sender) {
        try {
            const senderDecodeResult = await nip19.decode(sender);
            const { data } = senderDecodeResult;
            return data;
        } catch (error) {
            throw new Error(`Failed to decode private key for sender ${sender}: ${error.message}`);
        }
    }
Get the private key for the sender
@param {string} sender Sender to retrieve key for
@returns {nip19.DecodeResult} Private key