Cargo Bikes

The trick is to add a few more layers of tape so the tyre is a tighter fit. Once you have the right amount of layers it should air up without sealant and pop pop pop onto the rim. I then open a section of the bead, pour in the sealant, and air up again before shaking the sealant around.
Without enough tape, non tubeless tyres just piss the air out.

Edit. I should add that I use a pump with a tubeless chamber built in. I don't know how doable it would be with a regular track pump.