Google Ads measures to the day of the Click, Google Analytics to the day of the Sale.

Google Ads only considers Google Ads Clicks, Google Analytics use Multi-Channel attribution that by default gives 100% credit to the Last In click. So if the Google Ad drives them to the site, then they visit an Affiliate site to grab a coupon, Google Ads credits the PPC click, Google Analytics credits the coupon site with 100% of the sale.

There are more details and reasons here:
[support.google.com...]
[support.google.com...]

They measure different things, and they measure them differently.
I hear a lot of people declaring that they want to have "one source of truth".
As noble and compelling as this sounds, it's just dumb.
You have these two different tools (and you should have many others) reporting different things in different ways, NONE of which are more TRUE than the other.
Neither is inherently more accurate.

In you car, you have a tachometer, an odometer, a speed indicator, an oil temp gauge, and a gas level gauge... turn signal indicators, battery charge, seat belt use, air bag status... if you tell me you only want to use one of them, and you intend to dismiss all of the others in favor of a single indicator of your progress, well then you're an idiot or intentionally complicit in driving dangerously. :-) Yes, people will say "well, i would use the speedometer as my sole measurement for speed", and I would counter that I just made the same argument... depending on what you want to measure, there certainly is a best choice for that one KPI, but that one KPI paints too simple a picture of driving the car, or operating an eCommerce website... you need to use BOTH the metrics tracked in Google Ads AND those tracked in Google Analytics, to get a more complete picture of what is actually happening. There is not one source of truth for optimizing performance of your website. Those who insist that there is one are similar to the person driving their car with duct tape covering all of the instruments except one. :-)