“Sold” is the comment a customer writes on a live to claim an item, usually together with the item’s code (“sold 103”); the first one to write it gets the item, and the next ones go on the waitlist.
“SOLD” plus the item number is the classic way to claim an item on a live. Customers also write “mine”, “I’ll take it”, or just the code.
In LiveShopia what counts is the claim code, not the word: “sold 103”, “103” and “I’ll take 103” all reserve item 103 the same way, in comment order. Without a code, “sold” on its own reserves nothing, because it does not say which item.
Full guide: How to sell clothes on TikTok Live: prep, claim codes, orders, shipping