Merrian-Webster: a market employing irregular but not illegal methods especially : a market that legally circumvents authorized channels of distribution to sell goods at prices lower than those intended by the manufacturer https://www.merriam-webster.com/dictionary/gray%20market
Investopedia: A grey market is a market in which goods have been manufactured by or with the consent of the brand owner but are sold outside of the brand owner's approved distribution channels—an activity that can be perfectly legal. In the securities markets, a grey market is a market wherein a company's shares are traded before they are issued in an initial public offering (IPO). https://www.investopedia.com/terms/g/greymarket.asp
Wikipedia: A grey or gray market (sometimes confused with the similar term "parallel market")[1][2] refers to the trade of a commodity through distribution channels that are not authorized by the original manufacturer or trade mark proprietor. Grey market products (grey goods) are products traded outside the authorized manufacturer's channel. https://en.wikipedia.org/wiki/Grey_market
Conclusion: Grey market seems to be the correct term.