public function getInterests(array $interests): array
    {
        $tokens = [];

        foreach ($interests as $interest) {
            $retrieved = $this->repository->retrieve($interest);

            if (!is_null($retrieved)) {
                if(is_string($retrieved)) {
                    $tokens[] = $retrieved;
                }

                if(is_array($retrieved)) {
                    foreach($retrieved as $token) {
                        if(is_string($token)) {
                            $tokens[] = $token;
                        }
                    }
                }
            }
        }

        if (empty($tokens)) {
            throw ExpoRegistrarException::emptyInterests();
        }

        return $tokens;
    }