Alright, so if I understand you correctly, up until now when you have not had the need of presenting the payment date, there has been no problems, but since you've been asked to include this, you have hit a "performance wall"?
Regarding the 10 requests parallel, according to tests made by one of our users, the best performance is reached by running 10 parallel requests, meaning make sure that you do not just have 1 request going at a time, but say that you have 12 pages you need to get, send the request for those first 10, whenever any of the requests are done, send of the next one and so on.
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