That rate limit is imposed by the Trello API; the only solution for you is to either
(i) fetch lists of members rather than individual members (if the API provides that endpoint)
or
(ii) work around that rate limit by handling the exception appropriately and pausing execution through the array while the rate limit prevents further requests
You are probably running up against rate limits from your earlier attempts - max. 100 requests per 15 minutes is going to take a while to decay! I would suggest to create a Job which batches the member ids, and put them on a Queue in a manner that will not run up against the rate limit.