American law International Traffic in Arms Regulations, commonly known as ITAR, prohibits the export of strategic materials and their technologies. Rocket technology belongs to ballistic missile-related technologies, and the items involved also overlap with those of ballistic missiles, so even NATO and other allied countries are The export is prohibited, which is basically the same as the control of dual-use items in my country.
In addition, the MTCR (Missile Technology Control Regime) at the level of international law also restricts the export of missile-related technology by signatories. The United States is one of the signatories. (Not China)
In addition, the US law Export Administration Regulations (Export Control Regulations) has made a more detailed elaboration on the definition of "export", almost all items related to rockets, whether it is sale, transfer, related design, process, data, blueprint, zero Components, essentials of knowledge, talents, flow into foreign territory by any means, means of transport, or computer equipment under the control of foreign persons shall be considered as exports.
So the rocket can't be sold.
The Electron rocket launched by Rocket Lab in New Zealand is a special case. In order to cooperate with the company, the New Zealand government did not hesitate to legislate to "cede" part of the sovereignty of the launch site to the United States in a borderline manner. Export is legal.