Kiln dried sand
That’s the stuff mate

i`ve used once something like "silicon sand for patios" or "silica sand for patios) but im not sure the real name. it looks like regular sand (you just brush it in joints) water it down slighly and then it kind of melts and seals as "rubber".

You can also use a jointing compound little more expensive but less chance off it coming out on the next wash/ clean .

Kiln dried san is the best stuff to use, and can be bought fairly cheaply from most DIY merchants - some even call it block paving sand.
The easiest process is as follows;

1) Spread a thin layer of sand evenly over the tops of the pavers.
2) Sweep the sand into all the spaces between your pavers, starting on one side and working your way toward the other. Use the broom to push the sand between the paving stones, sweeping in all directions until the sand is relatively compacted.
3) Sweep any excess sand off of the surface of your pavers. Use a light touch, in order to avoid disturbing the sand in between the pavers.
4) Turn on your hose and set the spray nozzle to low. Spray the pavers with water to help pack down the sand in between the pavers and wash any remaining sand from the surface. Allow the pavers and sand to dry completely.
5)重复,直到所有的关节都充满了严格的compacted sand.

You don't have to seal it by right, but for longevity it can help. Simple sealant is easy to come by from most shops.

Just brush in sharp sand. You don’t need a sealant