Typically all you need to do is get the gray lockring more tight on the install. This is the main thing preventing motor rotation. The tighter it is, the more friction you are adding to prevent rotation.
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Ideally you also want that block lockring to be in use as well, this acts as a jam nut to prevent the gray lockring from loosening up.

You do want to make sure that the teeth of the black triangle mount is facing against the bike frame (it needs to be facing the bottom bracket shell). These teeth bite into the metal on the frame and helps keep it in place.

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If there is a gap between the mount hardware, you need to fill that in with spacers, otherwise the teeth on that plate will not fully contact the bike frame.
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In this picture the black triangle mounting bracket is NOT flush with the motor, there is a 1mm gap. You should add washers until there is no gap. If you do not do this you will have problems keeping the motor in place. The black triangle mounting bracket MUST be flush with the motor. If you buy from Luna we include some spacers you can use. If not or they are not the right width then you should use washers. There should absolutely not be a gap here, if you tighten it without making it flush the bracket will not bind properly with the bottom bracket shell and the motor will move around when under load.

If nothing works or you are still having problems

There are alternate mount options available, referred to as BSB-1 and BSBF-1. Likely you do not need this if you follow the advice above, but if you want to make absolutely sure you can use one of these mounts.

Mount style is a bit different and one or the other may be more suitable depending on the frame you have, width of the bottom bracket and so on. Most people just need the BSB-1 though.

BSB-1 stabilizer bar

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BSBF-1 stabilizer bar

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