UFC 257 was a massive success, reportedly being one of the highest ever drawing events with a reported 1.2 million pay-per-view buys in the US, along with an added 400,000 purchases from abroad. Conor McGregor may have lost to Dustin Poirier that night, but he did bring the UFC a significant amount of revenue.
Veteran reporter Dave Meltzer discussed PPV buy rate on his Wrestling Observer newsletter:
That number would be a figure not including refunds, and while nobody knows the number, there were a significant number of people who asked for and got refunds.