Which country should I buy a node in
Cross-border stores don't require a particular country. A store under a local company should use the same country as the company, or a nearby one.
Which country to buy depends on whether the store is cross-border or under a local company. To add a node, see Add a node. For which type, see How to tell node types apart.
Cross-border stores
Stores such as Amazon Global Selling and TikTok Shop POP do not require a particular country for the IP. You do not have to buy a node in the marketplace country.
For a seller in mainland China whose company is registered in mainland China or Hong Kong, a Hong Kong node is the usual pick. From mainland China, a Hong Kong node is faster — launching and opening the seller dashboard is smoother.
Stores under a local company
If the store is under a local company, the node should match that company's country, or a nearby one. A US company running a US store should buy a US node.
If you later change the node, keep it in the same country when you can. See Is it risky to change a store's node.