Is RHA 4 okay to use for lip filler? I can't found any info about it.

RHA-4 is a deep volumizer, and would not be my first choice for lips. RHA-1, which goes by Redensity in the U.S., is my recommendation.

After reviewing with our nurse injector, our injector responds with the following:

RHA® 4 isn’t really recommended for lips. It’s a thicker, firmer filler that’s better suited for areas like the cheeks or jawline where more structure and support are needed. Because the lips are soft and move a lot, using something too dense like RHA 4 can make them feel or look unnatural. Instead, RHA® 2 or RHA® 3 are much better options for lip filler—they’re designed to be more flexible and give a softer, more natural result that moves well with your expressions. If you're thinking about lip filler, it's best to stick with one of those and talk to your injector about what will work best for your look.

Technically, this filler can be placed in lips, though is an off-label use. I have used Voluma before in lips in a runner who chewed through her fillers very quickly with good results. However, it is a firmer product and you may notice and feel it more. You might try a small amount first to see how you like it.