This is embarrassing to ask.
Just changed my camera to an Olympus OM-D-E-M5 II and bought a Cactus system to go with it, an LV5, 2 x V6 and 2 x RF60 units as I prefer manual flash. Using the V6 units as wireless remotes outside presented no problems, very pleased. Today I tried one of the flash units indoors and, although the flash fired when asked it did not illuminate the subject, even at 125th at F8, no banding on the image, no illumination at all. Can anyone help, am I missing something simple.