Yes. The EOS 6D cannot trigger off-camera flashes by itself, so you’ll need an external trigger method.

Your main options are:

• Canon optical master flash: A small unit like the Canon 90EX can mount on the camera and command the 430EX III-RT in optical slave mode. This can work well, but optical triggering needs line of sight and can be unreliable in bright sunlight.
• Radio trigger: You can use a third-party radio flash trigger, which is often much cheaper than Canon’s own transmitter. This is usually the most flexible option for off-camera use.
• Off-camera TTL cord: A Canon-compatible E-TTL off-camera cord gives a simple wired connection if you don’t mind being physically tethered.
• Another compatible flash on-camera: A second flash that can act as a master can trigger the 430EX III-RT.

If you want the easiest low-cost setup, a third-party radio trigger or an off-camera cord is usually the practical choice. If you already have or can find a cheap Canon 90EX, optical control is also a workable solution with the usual optical limitations.