Customer double charged on website. Code issue?

Hello. First, I'm having trouble getting in touch with my web designer. Probably very busy. First I have a question.

Is it possible for someone to be double charged because of a button error in the code? Or is it most likely a customer error? Now, Its a new site and I had 3 sales. The last one was double charged. The other 2 were fine.

My other question is am I allowed to link my site on this forum? I don't want to make it seem like I'm advertising.

I saw the pinned post. Looks like some sort of app that helps with web design and find broken links. Honestly don't have the time to learn this stuff but is it necessary for more forum help? If so I'll see about looking into it.

You can put your website into your forum signature.

Or, if part of a question where it makes sense, simply type the website address without as link.

See https://webhelpforums.net/forum-announcements-questions-and-discussions/forum-rules/

Can't you see in your system what charges you passed on. I assume you are using an API for card processing? That should give the answer if it's a bug or not.