Hello user62445,
Thank you for reaching out to Constant Contact API Developer Support. My team is here to assist outside software developers with questions about building into Constant Contact's API.
It looks like we've already followed up with you directly via email, but here is the information provided for visibility on the forum:
As with most APIs, our API has rate limits to help maintain stability and security. Our standard API access has a rate limit of 10,000 calls per day, and 4 calls per second. Once your key has hit its limit, your calls will see this error until the next day (or the next second if going over your queries-per-second limit)
429: Too Many Requests
https://v3.developer.constantcontact.com/api_guide/glossary_responses.html#429-too-many-request
To avoid the queries per second error response, You could set up your application to only make synchronous refresh calls with a 1 second latency, having code execution wait for the API call to return and wait a full second before allowing another request.
If you are planning on making an application that would be available and potentially used by a large base of customers then I would suggest you look into becoming a Technology Partner with Constant Contact. There is no price involved with this and the basics are to just create and maintain your app, though there are other parts to it. Members of our partner program are given 250,000 calls per day and up to 10 calls per second. To associate your API Key with a partnership, you can look into becoming a Technology Partner: https://www.constantcontact.com/partners/technology
Also, if you'd like any insight or suggestions on cutting down on the amount of calls used based on the data that your application sends/receives, please feel free to send us an example of the endpoints you're calling and/or what specific data you need for each account and we're happy to take a look and see if we can suggest a way to use fewer endpoint calls to accomplish the same task.
Please have a look and let us know if you have any other questions!
Regards,
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