We apply API rate limiting, so use bulk calls where possible!
If you're looking to import or update multiple contacts at once, then we highly recommend using Bulk import contacts instead.
It allows you to import a collection of contacts and has the benefit of being a single API call only, making it far less likely that your account will exceed its API calls per hour limit.
Need to add contacts to an address book as well?
The following methods can create/update a contact whilst adding them to an address book therefore saving time and API calls.
This operation creates a new contact or updates an existing contact within the account and adds it to the 'All contacts' address book.
Setting the OptInType to 'VerifiedDouble' will result in a double opt-in confirmation email being sent to the contact. The result will state that the contact's OptInType is 'Double' and Status is 'PendingOptIn'. These will only update to 'VerifiedDouble' and 'Subscribed' respectively once the contact has clicked the link in the confirmation email, at which point they will be added to the account.
Note that it is possible to update an existing contact using this operation. A duplicate contact will not be created. If the contact already exists, then any data provided in your request that is already held for the contact will be overwritten and updated in the system.