I tried to create interaction between FLIP and Grains, In my simulation, the FLIP pushes the grains, but the grains don't affect the FLIP particles (it seems one direction collision)!
How can I fix it? And is there any tutorial about the interaction between FLIP and Grains?
They are two separate systems. Just use pop fluid instead, which is kinda like SPH in the xPBD world. That way you will get two-way interactions, it's actually quite good.
Pop fluid is under appreciated, considering what it is doing.
To solve the problem, I created a "collision" SDF from grains points, and then by using a "Volume Source" DOP node, I applied "collision" and "velocity" to the "Volume Velocity" input of FLIP Solver, and it work like charm.