Use ActiveCampaign's Contacts API to sync a contact list with tags and custom field values, implementing upsert logic using the sync endpoint and handling field type validation
POST /api/3/contact/sync with a JSON body containing 'contact' object (email, firstName, lastName, phone) and 'fieldValues' array of objects with 'field' (field ID as string) and 'value' to upsert the contact
Retrieve field IDs by GET /api/3/fields to build a mapping from field names to IDs before syncing
Apply tags by POST /api/3/contactTags with 'contactTag' object containing 'contact' (contact ID from sync response) and 'tag' (tag ID); retrieve tag IDs via GET /api/3/tags?search={tagName}
Handle the 'fieldValues' validation: date fields require YYYY-MM-DD format, checkbox fields require '1'/'0' strings, and multi-select fields require pipe-delimited values (e.g. 'optionA||optionB')
Verify the upserted contact by GET /api/3/contacts/{id}?include=fieldValues,contactTags to confirm all fields and tags were applied
Known gotchas
The /contact/sync endpoint matches on email address only — if the email changes between syncs it creates a new contact rather than updating the existing one; handle email changes by first looking up the old contact and explicitly updating the email field
ActiveCampaign enforces field type formatting strictly at the API level; sending an incorrectly formatted date or an out-of-range option value returns a generic 422 error without specifying which field failed
Tag IDs are numeric and must be resolved before use; the sync endpoint does not accept tag names directly, and creating a new tag via the sync body is not supported — tags must be pre-created via POST /api/3/tags
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