moment JS returning NaN on common date

I’m trying to get thisDate in milliseconds using moment.js and I’m getting NaN when I run the valueOf() method. I’m honestly clueless as to why this isn’t working considering my date is a pretty standard date.

const thisDate = '18/07/2023'
  
console.log(moment(thisDate).valueOf())

<script src="https://momentjs.com/downloads/moment.js"></script>

I’ve tried the same with multiple other dates and the result is random, some dates will output the value in milliseconds correctly others will just return NaN.

What am I doing wrong?