Sorry for the confusion, the "C" in HK3-C actually indicates a type-C port, in order to tell that apart from the previous MINI USB HK3 used in A119v3 and A129 series.Probably why Viofo doesn’t show it on their website ;-)
The standard hardwire kit for A139 PRO is HK3-C, the same as A139; you can also use the HK4 on A139/A139PRO, as it is also a type-c port, while its port angle is right, not straight as HK3-C, you can tell by the pics.
You may contact us directly by the below method if any other issues.
Submit a ticket
support.viofo.com