Issue seeing tethered viewfinder image A7R ii w flash

Using flash and shooting tethered, if I set the exposure in Manual on my camera (Sony A7R ii) the image in the viewfinder or on the screen is too dark, but if I open up to see image, the file I take is overexposed. Thus useless for portraits.
What am I doing wrong?
This has never been an issue on Canon 5Dx.
Thanks