If you receive an "Error 500" message when visiting your Checkout page, this usually means there's an error in the communication between your site/checkout form and your Stripe account
Most commonly, this occurs because you had a product set in TEST mode, and you disconnected test mode but did not change you product to LIVE mode
Firstly, an important note:
You do not need to disconnect test mode on your site at any time - this mode can be left connected and just switch your products to LIVE mode when you are ready to sell them to the public. Disconnecting test mode on your site will result in any checkout forms which are connected to products in TEST mode showing an error like error 500
If you experience this on one of your checkouts, the first thing to check is the Payment Gateways setting for your product:
1. Go to OptimizeCheckouts > Products > and select your product that you're selling on the checkout page
2. Go to Payment Gateways option
3. Check the dropdown is set to the correct mode - If you want to sell the product to the public, this must be set to Live mode. If you do not see Live mode available, you must first connect Stripe in live mode.
4. Click Save (VERY IMPORTANT)
5. Go to retest your checkout page and you should find it now works correctly
