Rule of thumb: Pick file feeds over API feeds unless you have reason not to. If API feeds is really needed, make sure you read on for all the pitfalls.
API feeds update individual products data change (prices, stock, description, title) instantly. API feeds are run
1/ When a new feed settings is saved (including new feeds creation).
2/ For individual product changes that trigger webhooks (please read on for webhooks' limitation)
3/ When manually requested from the app dashboard (please be aware of Google's recommendations about not running API feeds too regularly).
4/ API feed fully re-run after every 30 days, to make sure that unchanged products do not expire in Google Merchant Center. You can also schedule more frequent API feed renew at additional cost.
A Google account that has access to a GMC needs to be connected to the app to authorize access to the GMC.
The connected account needs to retain the access to the GMC. Otherwise, the app would also lose its access and API feeds will no longer work.
The authorization should also be kept, as many has accidentally revoked the app's access after granted.
API calls are made between servers and are prone to temporary errors (network, server condition, account access)
Since API calls are rate limited by Google API, API feeds are not suitable for cases that require mass product updates, including the initial run and regular re-new runs. This means API feeds cannot be used for foreign currency feeds as it requires mass price updates when the exchange rates fluctuate.
Shopify webhooks may not fire. API feeds depend on Shopify product webhooks to learn about product changes to start synchronization. Since webhook delivery isn't always guaranteed, products might not get synced for all changes. (please read more about webhooks' limitations). Also, only these product changes trigger a webhook (and therefore get synchronized by an API feed):
Product creates
Price, stock, title, description and metafield updates
Exchange rates (Shopify Market) and product data translations change do not trigger API feeds
In most cases API feeds do not remove products. Products no longer in feeds are just stop synchronized and left in Google Merchant Center for expiry (default to 30 day since last update).
API feeds are not tangible so it's difficult to troubleshoot.
File feeds (TSV, XML) should be preferred than API feed in most cases
API can be used to work with file feeds, or in most case, just the file feeds are enough.
File feeds (XML, CSV, TSV) do not update individual products, but every time they run, they update the whole portfolio part that is included in feeds. Because the file represent all the items at any time, items no longer in the file feeds are also removed from the targeted platform, which is important in cases.
Items are no longer in the file feeds are removed from the targeted platform after refetch
File feeds are not subjected to Google API rate limits so they are much faster than API feeds for mass updates, that is why they are recommended for foreign currency feeds. In fact, file feeds are suitable for most of the use cases, even for fast stock changing portfolio (Google bot can help to sync individual stock updates by crawling the landing page). File feeds are run:
1/ When a new feed settings is saved (including new feeds creation).
2/ At least once every 24 hours at configurable time of day. Additional runs are possible at addition cost.
3/ When manually requested from the app dashboard
File feeds are more stable than API feeds in most cases. Besides, since a tangible file is generated at the feed URL, it is easier to troubleshoot any feed issues.
If a file feed is connected to a GMC through a connected account, it is added automatically to GMC at creation time. After that, even when the account is disconnected, GMC can still fetch the added feed URL.
GMC access is not constantly required on a file feed
You can have the best of both file and API feeds by having the file feed as the primary feed and create a supplement API feed. A feed rule is then created (automatically) in GMC to tell Google to use the updated data from the API feed when it's available.
This setup will then allow your portfolio to be updated (price, stock changes, etc.) instantly by the API supplement feed. In any cases when API feed is not working (due to above shortcomings), the file feeds get run at least 24 hours. As the file feeds are created as the primary feed, it will also make sure that obsolete products get removed.
Adding more feeds might require plan upgrades. However in cases where your store has a lot of products, the additional feed might have already been covered in your current plan.
