Use map instead of forEach with a firestore snapshot

map-snapshot.js

exports.recurringPayment = functions.https.onRequest(async (req, res) => {

  const hook = req.body.type
  const data = req.body.data.object

  // 300 or 400 as failed will cause stripe to rerun
  if (!data) return res.status(400).send('data missing')
  if (!data.subscription) return res.status(200).send('not a subscription')
  if (hook !== 'invoice.payment_succeeded' && hook !== 'invoice.payment_failed') return res.status(400).send('unknown hook')

  const status = hook === 'invoice.payment_succeeded' ? 'active' : 'pastDue'

  try {

    const doc = await admin.firestore().collection('subscriptions').doc(data.subscription).get()

    await Promise.all(snapshot.docs.map(async doc => {
      try {
        await admin.firestore().collection('subscriptions').doc(doc.id).update({status: status})
        await admin.firestore().collection('users').doc(doc.data().uid).update({'subscription.status': status})
        return res.status(200).send('done')
      } catch (error) {
        console.log('admin.database().collection(subscriptions).doc().update()', error)
        return res.status(400).send(error.stack)
      }
    }))

  } catch (error) {
    console.log('admin.firestore().collection(subscriptions).where().get()', error)
    return res.status(500).send(error.stack)
  }

  return res.status(200).send({
    message: `success`,
    query: req.query,
    data: data
  })

})