Getting 429 Too Many Requests on the campaigns API

Yep — the API is limited to 60 requests per minute per API key. At 3,000 contacts that'll definitely trip it if you're firing requests as fast as possible. A couple of options:

• Add a short delay (roughly 1 second) between requests to stay under the limit.
• Use the bulk contacts endpoint instead of one request per contact — it accepts up to 500 contacts per call, so 3,000 contacts is 6 requests instead of 3,000.

The response also includes a Retry-After header when you do get a 429, telling you exactly how many seconds to wait before retrying.

Just 1 request against the limit, regardless of how many contacts are in the payload (up to the 500 max). So batching is strictly better for both your rate limit budget and your total request count.