Checkout page error

Hello, whenever I try to make a payment on my website, I get this error message. At first, I thought it was the payment gateway I was using, and then I added another one. Still, the same problem persists irrespective of the payment option chosen on the website.

I sent a mail to my hosting company(a2hosting). They replied that the problem isn’t from them, and I should message the developer. I’m using paystack and flutterwave, and both payment gateway gives the same error, so I’m a little bit sure the problem isn’t from them but WordPress. My website link, you can try making payment and see the error I’m getting. Please I need assistance immediately, kindly assist me. Thank you.

The page I need help with: [log in to see the link]