Hi, @pimsandra !
Thanks for reaching out to us about this.
First off, you can reach our general support lines such as live chat here.
With that said, I am more than happy to assist you via this thread as well. Can you tell me a bit more about the steps you are following when you are seeing the "Bad Request" error message at Checkout? Does it appear when the payment method is entered? Does it occur when you use different web browsers as well?
If you can give me a bit more context, your store URL as well as a screenshot of the error message, I'd be happy to look into it for you.
I look forward to your reply.