Hello.
If you use a non-modified version of Authorize.Net make sure you have Fast checkout enabled. Additionally, when encountering an error, please inspect both the browser's console log and AbanteCart's error log for insights. Could you specify if the error appeared upon loading the payment page or after submitting the card details?

Hello.
Modify the /extensions/bootstrap5/storefront/view/bootstrap5/css/style.css
add CSS rules to the top of the page for example
.navbar.navbar-expand-md.navbar-dark.bg-dark {
    background-color: red !important;
}

Hello.
What is your AbanteCart version?

Hello.
You don't need a direct link to access the Package Installer. Simply go to Extensions > Install Extension in your dashboard. Also, while there could be various reasons for outgoing emails not functioning properly on your hosting, it's advisable to ensure you're using the latest version of AbanteCart for optimal performance.

Hello.
You need to replace the link to font-awesome.min.css

hello. I have already done all 3 ways either in https and http and nothing works for me. I still have that problem

Hello. What is your store URL?

Hello.
You change the default settings and that's why it does not work as configured by default
Processing Controller: Contact us page
Success page: content/contact/success