You need to put more water when mixing up your soil, grab a handful if it clumps together good it is right. you want a thick brownie texture. Experiment. Look up Eliot Colemans mixture for plane starting, it is a good mix.

I’ve only used them twice now, but the key to making it work is packing a lot of soil in the blocks. Make sure they are full and packed tight. Also, you might try putting them in a tray (with holes in the bottom) where they fit perfectly and then placing that tray inside a larger one and then watering from the bottom of the larger tray and allowing the water to soak up into the soil of the smaller tray. That way there isn’t soil “interacting” directly with the soil in the blocks.