handleApiError(error) {
        if (!error.response) {
            return error.message;
        }
        switch (error.response.status) {
            case 400:
                return "Invalid recipient identity or account not set up for basic mode (400).";
            case 401:
                return "Incorrect API identity or secret (401).";
            case 402:
                return "No credits remaining (402).";
            case 404:
                return "Recipient not found (404).";
            case 413:
                return "Message is too long (413).";
            case 500:
                return "Temporary internal server error (500).";
            default:
                return error.message;
        }
    }
Handle Threema API errors
@param {any} error The error to handle
@returns {string} Additional error context