JupyterLab keeps giving a syntax error for else when there are no indentation issues

I am trying to run this code but Jupyter keeps giving me the following syntax error at the else condition.

File "<ipython-input-24-beb6bcd9d77b", line 24 else: ^ SyntaxError: invalid syntax

I was running a similar code earlier and else worked there but I don't understand what's wrong with this code.

valid = True

while valid:
    
    if predators != 0 and prey != 0:

        preyCount.append(prey)
        predatorCount.append(predators)

        prey = prey * (1 + preyGrowth - predationRate * predators)
        predators = predators * (1 - predShrink + predFedBirthRate * preyCount[-1]
        
    else:
        
        valid = False