Events.php

    $contributionRecur = $this->getRecurFromSubscriptionID($subscriptionID);
    if (empty($contributionRecur)) {
      // Subscription was not found in CiviCRM
      $result = [];
      \CRM_Mjwshared_Hook::webhookEventNotMatched('stripe', $this, 'subscription_not_found', $result);
      if (empty($result['contributionRecur'])) {
        $return->message = $this->formatResultMessage(__FUNCTION__, E::ts('No contributionRecur record found in CiviCRM. Ignored'));
        $return->ok = TRUE;
        return $return;
      }
      $contributionRecur = $result['contributionRecur'];
    }

    if (!isset($stripeData->previous_attributes)) {
      // Nothing changed?!
      $return->message = $this->formatResultMessage(__FUNCTION__, E::ts('No changes. Ignored'));
      $return->ok = TRUE;
      return $return;
    }

    // First work out what changed. This is held in "previous_attributes" on webhook data
    $previousAttributes = $stripeData->previous_attributes;
    // Simple check that we actually have some items data
    // Otherwise it could just be a metadata change which we are not interested in.
    $amountHasChanged = FALSE;
    if (!empty($previousAttributes->items->data)) {
      $amountHasChanged = TRUE;
    }

    if ($amountHasChanged) {
      $subscriptionItems = $stripeData->object->items->data;
      $calculatedItems = $this->api->calculateItemsForSubscription($subscriptionID, $subscriptionItems);
    }

    // $calculatedItems now contains array of new prices by key [currency]_[frequency_unit]_[frequency_interval]
    // Eg. $calculatedItems[usd_month_1] = [
    //       'currency' => 'usd',
    //       'amount' => '2000', (amount is in pence)
    //     ];

    // Now check if recurring contribution matches frequency
    $contributionRecurKey = mb_strtolower($contributionRecur['currency']) . "_{$contributionRecur['frequency_unit']}_{$contributionRecur['frequency_interval']}";
    if (isset($calculatedItems[$contributionRecurKey])) {
      $calculatedItem = $calculatedItems[$contributionRecurKey];
      $templateContribution = \CRM_Contribute_BAO_ContributionRecur::getTemplateContribution($contributionRecur['id']);
      if (!Money::of($calculatedItem['amount'], mb_strtoupper($calculatedItem['currency']))
        ->isAmountAndCurrencyEqualTo(Money::of($templateContribution['total_amount'], $templateContribution['currency']))) {
        // Create a new template contribution to update the amount
        ContributionRecur::updateAmountOnRecurMJW(FALSE)
          ->addWhere('id', '=', $contributionRecur['id'])
          ->addValue('amount', $calculatedItem['amount'])
          ->execute();
        $return->message = $this->formatResultMessage(__FUNCTION__, 'recur: ' . $contributionRecur['id'] . '; new amount: ' . $calculatedItem['amount'] . ' currency: ' . $calculatedItem['currency']);
      }
      else {
        $return->message = $this->formatResultMessage(__FUNCTION__, 'recur already updated: ' . $contributionRecur['id'] . '; amount: ' . $calculatedItem['amount'] . ' currency: ' . $calculatedItem['currency']);
      }
    }

    $return->ok = TRUE;
    return $return;
  }

}