Did you copy files directly to root sd card folder? If you place them within any subdirectory it won't update.
A129 Plus firmware update contains following files:
FWA129S.bin (for front camera with Build version info)
FWA129SN.bin (for front camera with Build2 version info)
FWE129S.bin (for front camera - eMMC version)
RearcamA129FW.bin (optional, for rear camera)
RearcamA129FW.update (optional, for rear camera, this file size is zero byte)
If you copy all FWA129S.bin, FWA129SN.bin and FWE129S.bin files to root directory of SD card, then device will choose correct one for it's update.
Not all firmware updates contains rearcam update. For example, latest one V1.8 does not include it, while previous one V1.6 did.
There is V1.7 (Rear: V1.7_20210416) rearcam update included in V1.6 firmware update package.
Currently there is no way to download V1.6 with rear camera update files from global Viofo site, but someone shared all official A129 Plus rear camera updates here:
https://drive.google.com/file/d/1D6zcIQ1x-r6YvvdFQSfh-CVLFOnCBhWs/view
You can also download V1.6 update from official Polish Viofo support site:
https://www.viofo.pl/FIRMWARE/A129PLUS/v1-6/FW-1-6.zip
I asked Viofo support about lack of V1.8 rear camera update files, which in fact exists. They told me that normally, they won't recommend users update the rear camera firmware if it works well. The firmware is just to fix some bugs. Thay did publish the rear camera firmware before, but there is no need to update it if everything is ok, so they cancel it on their website. Viofo support can send rearcam V1.8 update on request, and in fact they sent me RearcamA129FW.bin file with "Rear: V1.8_20220615" update.
Here is offical front camera update video tutorial:
To update rear camera:
1. Disconnect camera power supply
2. Copy RearcamA129FW.bin and RearcamA129FW.update (zero byte file size) to root folder of SD card
3. Make sure that rear camera is connected to front camera by cable
4. Connect camera power supply, make sure it won't turn off during update process (2-3 minutes)
5. When camera boots up, press camera switch button for a while. Message "Send FW to Tx..." will appear, then next one "Tx Start Update FW...". Wait until blue message dissappear. You can watch this procedure here
(Polish language, but it doesn't matter) or here
I found no issues with different front and rear camera versions. In my case front is "A129Plus: V1.8 Build2: 20220706" and rear was "Rear: V1.7_20210416". Everything worked fine. I had no time to update rear camera with V1.8 from Viofo support yet.