Hi Amanda,
SFDC related flow steps in Marketo make live API calls (Sync Lead to SFDC, Add to SFDC Campaign, etc). Depending on the flow step those can use between 1 and 8 API calls.
During a single sync session, Marketo makes 25 API calls to check if your Salesforce objects need updating. Because your Salesforce sync happens in 5 minute intervals (default setting), each day Marketo makes 7200 API calls to your account to see if any updates are needed.
If there are updates, more API calls are used to sync the information. Leads, Contacts, Accounts, Opportunities, Campaigns, and Activities are synced in batches of 200 per API call.
If you use a Sync Lead to SFDC or Add to Campaign flow step, each one uses one API call per lead; the API call happens when the lead hits that flow step (instead of waiting for the next sync).
Any activities you've synced from Marketo to Salesforce (like "Filled Out Form" or "Opened Email") use an extra API call per event. (You can see what events are syncing under Admin > Salesforce > Enabled Activities)
You can use these to estimate the number of API calls Marketo makes per day. For example, if you have 1,000 Lead and Contact updates a day and 100 Account, Opportunity, and Campaign updates, you'll use:
7200 (check for updates) +
(1000 Lead updates / 200 per API call) +
(1000 Contact updates / 200 per API call) +
(100 Account updates / 200 per API call) +
(100 Opportunity updates / 200 per API call) +
(100 Campaign updates / 200 per API call) +
7200 + 5 + 5 + 1 + 1 + 1 = 7213 API calls
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