Buyer not able to buy multiple quantities from my listing?

[dynamic.duo.collectibles]

I have a listing with multiple quantities, and a buyer contacted me today stating 'I am trying to purchase 4 orders and eBay won’t let me'?  Any idea what I need to do to enable the buyer to buy multiple quantities?  I checked an the buyer has been an eBay member since 2008 and has a 100% feedback rating?  Thx.

[woodland_gnome]

Check your Buyer Requirements  https://www.ebay.com/bmgt/buyerrequirements  to see if you have enabled a 10 day limit on purchases from you.   Also check your Buyer Requirements Activity Log (there is a link on that same page) to see if there is some other action on your part causing it.  You of course have no control over any buying limit or issue that eBay has with the buyer.

"I can't do xyz" is way too vague to do more than take guesses on.  We'd need to actual exact error message of a detailed description of what steps s/he is taking to  narrow it down.