Upsert leads into a data collection

Up to 1000 leads per request, applied through the same importer the CSV upload uses. A row that matches an existing lead updates it rather than inserting a second copy; the match column is the collection's primaryKeyColumn when it declares one, otherwise its phone column. Phone matching compares the last ten digits, so +1 (555) 100-0000 and 5551000000 are the same lead.

Rows are never rejected as a batch — the response tallies what was created, updated and skipped, and explains each skipped or malformed value in warnings. Rows that would take the collection past its plan row limit are refused individually and reported the same way; 409 is returned only when the collection was already over its limit and nothing could be written.

A collection owned by an integration (readOnly: true, e.g. Shopify) cannot be written to and returns 400 read_only_collection.