Hey there @SeoS1de!
Don here from Shopify.
There are a couple of reasons you might be encountering this behaviour with the use of PayPal as a gateway.
Would you be testing your PayPal payment option using the same PayPal account that is linked to your Shopify store?
Another possible cause might be if you are testing your checkout from within a store preview rather than from your live storefront.
It's also always a good idea to clear your browser cache and ensure it's as up-to-date to as possible when you're setting up and testing things like this.
If you check both of these possibilities and find that this issue persists I would advise you to reach out to PayPal support directly as they will be able to provide more info on what any error message means and they will have access to info on your account with them.
All the best!