The error 429: Too many requests
is related to quotas, since Google Sheets has a per minute quota of 300 to read and write per minute per project or 60 to read and write per minute per user per project. However, Google has a unpublish limit on how many requests you can do for a second. You can read more information about this error message here.
If you exceed a quota, you'll generally receive a 429: Too many requests
HTTP status code response. If this happens, you should use an exponential backoff algorithm and try again later. Provided you stay within the per-minute quotas below, there's no limit to the number of requests you can make per day.
Since you use a Google Apps Script
tag, I'm inferring that you are using Google Apps Script to read or write requests to a Google Sheet. If you are using some kind of loop, you can use a simple Utilities.sleep(milliseconds) to put the script to sleep for the specified number of milliseconds.
Or you can use "exponential backoff" as mentioned by @TheMaster. I found some articles and posts on how to do it that you can use as a reference.
- Google Apps Script Retry With Exponential Backoff
- GASRetry - Exponential backoff JavaScript implementation for Google Apps Script
- Exponential backoff