GuideStar APIs impose a strict throttling limit on APIs of no more than 120 requests per 60 seconds. A program that employs the APIs and exceeds that rate will receive 403 errors. This is an example from our API logs:
16:42:43.8350|DEBUG| Middleware.API.Openrasta.PipelineContributors.ThrottlingPipelineContributor|user X
@somedomain.com|https://data.guidestar.org/v1/charitycheck/59-2602772|Request rate limit of 120 per 60 seconds has been reached
Each node is set to allow no more than 120 requests per minute. With 3 nodes, this can effectively increase to 360/min when the Load Balancer perfectly distributes the requests; however, the rule of thumb is less than 120/min.
If for some reason your API request frequency exceeds the limit,if you can insert some delay in your code between API calls this error can be avoided.