Your specific error means that something is not configured correctly on your web server. For example, if you use Apache, did you install mod_ssl? (Setting up the SSL host on Apache without mod_ssl installed generates a poster error.)
Some additional guidelines for setting up a secure payment page:
1) Add sw so that if some loads are http://secure.foo.com/yourSecurePage , they will be redirected to https://yourSecurePage.foo.com . How to achieve this best depends on your web stack.
Secure all pages during the payment process. This helps increase customer confidence.
2) Remember that all included images and files on your secure page must be uploaded using https, or users will see warnings about “insecure” content on the page. Use either relative links or use links in the form / another _dir / image.foo or // asset_server.foo.com / images / foo.jpg. DO NOT use http://asset_server.foo.com/ ... (Of course, any other server must also support SSL for this to work.)
3) If you collect credit card information on the secure payment page, you must add information on how:
a) Your website is certified to comply with the PCI Data Security Standard credit card industry
OR
b) The collected credit card information is never stored on your server, it is sent only to your bank.
You may have such data indicated on another page, but you may want to have a link on the payment page itself, for example, "We are safe" or "Your information is safe." Depending on your audience, they can be quite intimidating in terms of sending credit card information to a website.
4) Use Google Analytics (free) or another tool that allows you to accurately determine the number of “abandoned carts” - the number of people who started ordering your product / service, but then did not complete the payment process - abandoning your shopping cart, not buying . This is a key metric for your site.
Remember that you can use Ajax to store data that a person enters as soon as they enter it into the field - you do not need to wait for the "Send" button. This method can give you additional information to understand at what point people abandon their carts.
The payments page and other final parts of the buying process are great places to give a potential customer a phone number for your merchants, the ability to chat, etc.
Happy sales
Larry