For some reason, it sometimes doesn't work, but I made a small change and now it works. The small change is replacing the checking if the keyCode is 32, with checking if the keyCode is either 32 or 'Space'. Here is the r###lting code, for the main function:

window.addEventListener('keydown', function(e) {
var playButton = document.querySelector('button.ytp-play-button');
var isKey1 = e.keyCode === 32; // Space
var isKey2 = e.keyCode === 'Space'; // Space
var validTarget = e.target === document.body || e.target === document.querySelector('#player-api');
if (validTarget && (isKey1 || isKey2) && playButton) {
e.preventDefault();
playButton.click();
}
});

For some reason, it sometimes doesn't work, but I made a small change and now it works. The small change is replacing the checking if the keyCode is 32, with checking if the keyCode is either 32 or 'Space'. Here is the r###lting code, for the main function:

window.addEventListener('keydown', function(e) {
var playButton = document.querySelector('button.ytp-play-button');
var isKey1 = e.keyCode === 32; // Space
var isKey2 = e.keyCode === 'Space'; // Space
var validTarget = e.target === document.body || e.target === document.querySelector('#player-api');
if (validTarget && (isKey1 || isKey2) && playButton) {
e.preventDefault();
playButton.click();
}
});

THANKS, NOW WORK!