@Dren Thanks for your reply, glad to help you. If need any further help in the future, be free to let us know. Good day.

@MTerry In general, the powerline adapters are sold as a kit, while there are some available as single unit, like the TL-WPA8630P and TL-WPA4220. https://www.tp-link.com/au/home-networking/powerline/...

@benand_idk You are welcome, if need more help, be free to contact us. Best regards.

@TP-Annoyed What is the hardware and firmware version of the Tl-WA850RE? Please ensure that the firmware is the latest one. And what is the OS version of your Mac High Sierra? Good day.

@Mauma Replied this thread you posted. https://community.tp-link.com/en/home/forum/topic/179150

@Mauma Hello, please ensure that you use the main router's wifi password to configure the RE200. And locate it 3 meters away from the main router to set it up....