Getting URL_ROLLING_THROTTLES_LIMIT_EXCEEDED for some requests

Getting URL_ROLLING_THROTTLES_LIMIT_EXCEEDED for some requests

Hello. I'm trying to retrieve the documents list and then get fillable fields information for each signed document. To do this, after retrieving documents list, I'm sending a GET request for each document to this url
'https://sign.zoho.com/api/v1/requests/' . $document['request_id'] . '/fielddata');

For some cases it actually returns the information, but for other cases it gives an error: URL_ROLLING_THROTTLES_LIMIT_EXCEEDED
For example, if I run this request for 10 documents, 1, 3, 7 might return the data, but the rest don't. On the second run it's different results.

What does this mean and how do i fix this?