Buyers who have opted for the OnePlus 6 trade-in program were seen getting multiple voucher breakups instead of a single voucher for the exchange amount. This is causing problems as the trade-in program allows using only one voucher. OnePlus is known to have acknowledged this issue and is working on a resolution.
https://www.notebookcheck.net/OnePlus-6-trade-in-program-throws-up-an-unpleasant-surprise.309588.0.html