I believe this is something that eBay implemented in 2019 for items in the Gold and Bullion categories -- bids over $500 may require some additional verification now.
If you intend to bid on gold, do not wait until the last minute to bid unless you have gone through verification.
If you are unable to go through verification using the app, try using a browser.
See this long thread:
https://community.ebay.com/t5/Selling/The-new-eBay-policy-on-GOLD-and-bullion-Buyer-MUST-be-verified...
Specifically, here:
https://community.ebay.com/t5/Selling/The-new-eBay-policy-on-GOLD-and-bullion-Buyer-MUST-be-verified...
"eBay has a 2-factor verification flow for buyers who are purchasing items in bullion, watches, and coins categories. This is designed to help ensure a safe and secure experience for both our buyers and our sellers, and as a result, some buyers may be asked to verify their account prior to placing a bid. Given the unique nature of these types of items, we want our sellers to feel confident when selling these items."
