How to Fix SharePoint Online REST API 429 Throttling Errors

Inspect the HTTP response headers when a 429 error occurs. Extract the integer value from the 'Retry-After' header, which represents the wait time in seconds.

Use a delay function (such as Thread.Sleep or Task.Delay in C#, or Start-Sleep in PowerShell) to pause your script for the exact duration specified by the Retry-After header.

If the Retry-After header is missing, implement a fallback exponential backoff loop. Start with a brief delay (e.g., 2 seconds) and double the wait time after each consecutive 429 error until the request succeeds.

Keep an eye on 'RateLimit' response headers in successful calls. These headers indicate your remaining API capacity, allowing you to proactively slow down requests before a 429 error is triggered.

Combine multiple smaller OData requests into a single $batch endpoint request. This significantly reduces the HTTP overhead and the number of individual calls evaluated against the rate limit.

If your automation uses PowerShell, utilize the 'Invoke-PnPSPRestMethod' cmdlet along with PnP batching methods to stream list items more efficiently without triggering limits.

When querying large lists, avoid fetching all items at once. Use the '$top' and '$skiptoken' parameters to retrieve data in manageable, paginated chunks.

Append the '$select' parameter to your REST URL to specify exactly which columns you need. Avoid using '$expand' on lookup columns unless absolutely necessary, as it heavily increases query complexity.

Modify your application logic to cache static or infrequently updated data locally. Avoid querying SharePoint repeatedly for data that has not changed since the last execution.