The Barter Bricks In WoW Dragonflight is a currency that you can use to buy a mount, pet, hat, and even profession blueprints. The NPC who will sell you all of this is called Ponzo and can be found in Zaralek Cavern (58.0 53.8 coordinates).
How to get Barter Bricks in Dragonflight? It's simple, you just need to reach Renown Level 3. Then, you can get Barter Bricks by completing unique Ponzo quests or a character found in Soil (/way #2133 55.6 57.4) will ask you to solve investigations using a Battered Dig map (purchasable from Ponzo) or a Lost Delve Map. For each puzzle solved, you will get Barter Bricks.
What can you buy for Barter Bricks on Wow? In exchange for 999 Barter Bricks, you can acquire a hat, but if you compliment Ponzo on the quality of his hat (by talking to him and clicking a dialog option), the price drops to 249 bricks. Additionally, you have the chance to get a very valuable mount and pet.