Preliminaries:

• Shopkeepers version: 2.16.4**
• Spigot version: This server is running Paper version git-Paper-794 (MC: 1.16.5) (Implementing API version 1.16.5-R0.1-SNAPSHOT**

• I have checked that my issue/question does not get answered by:
  • The documentation.
  • The FAQ.
  • The Known Issues.
• I have checked all open and closed issues, but none seems to fit my issue/question.

The issue:

display-name: '{"italic":false,"color":"white","extra":[{"bold":true,"color":"yellow","text":"LÁ MÙA THU "},{"color":"green","text":"III"}],"text":""}' lore: - '{"extra":[{"bold":false,"italic":false,"underlined":false,"strikethrough":false,"obfuscated":false,"color":"white","text":""}],"text":""}' - '{"extra":[{"bold":false,"italic":false,"underlined":false,"strikethrough":false,"obfuscated":false,"color":"yellow","text":"Thông số:"}],"text":""}' - '{"extra":[{"bold":false,"italic":false,"underlined":false,"strikethrough":false,"obfuscated":false,"color":"white","text":""}],"text":""}' - '{"extra":[{"italic":false,"color":"white","text":"Dùng để trao đổi các vật phẩm tại khu vực "},{"bold":true,"italic":false,"color":"light_purple","text":"Event"}],"text":""}' - '{"extra":[{"italic":false,"color":"white","text":"Được trao đổi tại "},{"italic":false,"color":"yellow","text":"/warp event"}],"text":""}'

display-name: '{"italic":false,"color":"white","extra":[{"bold":true,"color":"yellow","text":"LÁ MÙA THU "},{"color":"green","text":"III"}],"text":""}' lore: - '{"italic":false,"color":"white","text":""}' - '{"italic":false,"color":"yellow","text":"Thông số:"}' - '{"italic":false,"color":"white","text":""}' - '{"italic":false,"color":"white","extra":[{"color":"white","text":"Dùng để trao đổi các vật phẩm tại khu vực "},{"bold":true,"color":"light_purple","text":"Event"}],"text":""}' - '{"italic":false,"color":"white","extra":[{"color":"white","text":"Được trao đổi tại "},{"color":"yellow","text":"/warp event"}],"text":""}'

These are similar item, but 1 of them has '{"extra": at the beginning and it cause the item need to trade doesn't match.
How can I disable that check "extra" or do something to fix this problem?

The plugin compares item data like how Minecraft itself compares the items in trades, and there are intentionally no options to change that (change to the comparison logic would result in client-side glitches).
The plugin also does not modify the text data of your items, but will store it as it was provided when you originally set up the trades.

So since the item inside the shopkeeper does no longer match the item you are currently trying to trade, my guess would be that something changed on how you create those items in the first place:

• Most likely: Maybe the plugin you use to create the items changed something in an update.
• Some third plugin might dynamically modify the items on your server.
• In the past, there were cases in which server updates caused the text representation to change. But I am not aware of this being the case recently, at least on Spigot. I have no information on Paper or other server variants.

Regarding solving this: If you figure out if some other plugin changed something on their item representation during some update, or is involved in this item data change in some other way, you can bring this up to them. This issue likely not only affects the trading inside shopkeepers, but also trading in (modified) vanilla villagers or item stacking inside player inventories.

If the changes of the involved other plugin are fixed in stone, your only way forward would be to update all your shopkeeper trades that contain items affected by this issue, replacing the old item variant with the new one. There is no automatic tool yet to do that.

Closing this as no further information was provided.