I have set the Canon 430EX III-RT to wireless slave and both devices to the same channel, but the PW will not link and the link light stays on red. I have tried a PW Plus X and a PW Plus II but no luck.
No, not without a PocketWizard unit on the flash's hotshoe.
The Canon -RT triggering system and the PocketWizard triggering system use different frequencies (-RT uses 2.4 GHz; PocketWizard, in North/South America, uses 340-354 Mhz) and the systems also use different radio signal protocols. They're completely incompatible with each other and tuned to different bandwidths, so they're not going to talk to each other.
You have to put the 430EX III-RT into an on-camera mode (i.e., have both optical and RF slave modes off so it will only "listen" to the hotshoe for triggering signals, not an optical sensor or built-in radio trigger) and onto the hotshoe of a PW receiver/transceiver unit to pop it remote from a PocketWizard Plus X or Plus II.
Or you can get an -RT master unit to use on camera and ditch the Pocketwizards. This probably isn't a complete list (Chinese clone gear proliferates like rabbits), but -RT master units you can use include:
- Canon 600EX-RT
- Canon 600EX II-RT
- Canon 430EX III-RT
- Canon ST-E3-RT
- Yongnuo YN-E3-RT
- Yongnuo YN600EX-RT
- Yongnuo YN600EX-RT II
- Yongnuo YN686EX-RT
- Yongnuo YN968EX-RT
- Phottix Laso transmitter
- Jinbei/Orlit TR-611C transmitter
However if you're mostly building a radio TTL/HSS system from scratch, consider the following. The Canon -RT system is all speedlights with the Jinbei/Orlit RT strobes the only current choice for something bigger.
If you want broader system expansion options that include studio strobes and bare bulb flashes as well as speedlights, tons of features for cheap, and cross-brand TTL support for both Canon/Nikon and mirrorless (and you're OK with not-quite bulletproof Chinese gear), consider selling your -RT and PW triggers to fund a Godox X system. If you absolutely must have bulletproof, start a savings account or win the lottery to go Profoto Air. If your mirrorless system is Sony, and you don't have a fortune, you can also consider the Phottix Odin II.
If you have a Pocket Wizard (or any other type of wireless trigger) attached to the 430EX III-RT you need to take it out of wireless slave mode. In wireless slave mode the flash is ignoring the hot foot and "listening" to its internal 'RT' radio receiver for instructions. But your Pocket Wizard radio transmitter does not speak 'RT', it speaks 'PW'. The two different protocols are not compatible. To listen to the receiver attached to the hot foot of the flash (or the PC Terminal connection) the flash needs to be set the same way as if it were attached directly to your camera's hot shoe in manual flash mode.
If you don't have a receiver attached to the foot of the 430EX III-RT then your transmitter needs to be compatible with the 'RT' radio receiver in the flash. Canon's RT flash units (430EX III-RT and 600EX-RT) and transmitters (ST-E3-RT) or third party 'RT' units such as Yongnuo's 'RT' flashes (YN600EX-RT, YN600EX-RT II) or transmitters (YN-E3-RT) are 'RT' radios. The radios in your Pocket Wizards are not 'RT' radios, they use Pocket Wizard's own proprietary radio protocol.