private function validateMemberPaymentType() {
    /** @var \Drupal\node\Entity\Node $campaign Campaign node object. */
    $campaign = $this->getCampaign();
    /** @var \Drupal\openy_campaign\Entity\Member $member Temporary Member object. Will be saved by submit. */
    $member = $this->getMember();

    $campaignPaymentTypes = $campaign->get('field_campaign_payment_types')->getString();
    $memberPaymentType = $member->getPaymentType();

    if (in_array($memberPaymentType, explode(', ', $campaignPaymentTypes))) {
      return ['status' => TRUE, 'error' => ''];
    }

    return ['status' => FALSE, 'error' => t('Payment type does not match types: @types.', ['@types' => $campaignPaymentTypes])->render()];
  }