When spinning the wheel you have to wait for it to finish before spinning the slots again.
The game would feel much more fluid if every spin you’ve won was added to a separate counter on the machine. This way you could spend your spin credits any time you want and still roll the slots even while the wheel is spinning.
This would also increase the rate that spins can be potentially won so jackpots can be potentially won more quickly (so the odds might have to be reworked accordingly.)
The spins could be left in the machine for other players to scoop up or…
The spins could also stay player side only so that when you come back you have unused spins.
Luckily both can be made to only work server side so that neither can be exploited easily.