What is the total cost of the cart you're trying to test? Typically, if the cart is between $0.01 & $1, the charge will fail as Stripe has a minimum charge amount. If you are trying to process a payment that falls within that range, then I'd recommend trying a larger amount and trying again. If that's not it, then your store may be in testing mode, which you can confirm by going to Settings/Payment Providers. When you click "edit" for Stripe, you can see if "testing mode" is enabled. If it is, then disabling should resolve the issue.
As for Paypal, they only allow guest checkout with a credit card in select regions. With PayPal Express, the default is set to ask customers to log in to PayPal (or create a PayPal Account. You can enable guest payments to let customers pay with their credit card even if they don't have their own PayPal account. To enable this feature, you need to have linked your own credit card to your PayPal business account.
To enable guest payments, you need to change the settings in your PayPal account settings. Learn more about enabling guest payments at PayPal.
Note: In some countries and regions, PayPal requires that customers pay by using a PayPal account. To confirm whether this applies to the country where your business is located, contact the PayPal support team.
Let me know if you have any questions.