How to fix a 404 error during a sale?

[uniquelyyou]

My page is showing a 404 error in the middle of a big sale and now I'm losing customers. Shopify support can't help me because of something about an API. I don't understand any of these technical terms or what to do. But I'm desperate. I did so much work to get the site up for a sale and now for my first opportunity to drive sales, and I am screwed. Left me in literal tears.

[Nia]

Hi, @Uniquelyyou!
 
Thank you for reaching out. Are you able to send through a link to your website so we can replicate this 404 error on our end please?
 
Is it occurring on a specific page? 
 
If you have already reached out to Shopify Support, are you also able to let me know what you have been advised please?