In the extension /extensions/fast_checkout there is no possibility to set the fields or delete them, I believe that the modification must be done through a file manager on some file inside the fast checkout folder. can anyone give me some suggestions on which file to edit and how to do? thank you

All files that you can to change placed inside public_html/extensions/fast_checkout/storefront/view/default/template/responses/checkout directory.
You can try to change them, but we recommends to create a new template extension based on default template (try to use our "developer tools" extension and clone template as extension )
Then you can copy directory public_html/extensions/fast_checkout/storefront/view/default as new directory with your newly created template text id. And then you can enable your new template and feel free to change anything inside your's template tpls.
To see directory tree as example  you can look on bootstrap5 tpls inside 1.3.3 release.

Regards

You should to add column into table order_products manually via phpMyAdmin
See screenshot

just install xdebug php-ext and create profile.
See https://xdebug.org/docs/profiler for details.
Then open profile in the KCachegrind or some other profile analizer(for example phpstorm) and check what part of code run slow.

I don't see any other way to check.

try to use session. Set some value (current product url into $this->session->data['product_url']) and set it into your hidden field in the form

strange situation.
Looks like somebody broke this file public_html/admin/view/default/template/form/form_open.tpl
Try to edit it or replace with this

If not help - try to replace all content of this file with <form method="post">

i have verified my php sendmail functioning is working.  I get the below error still in the AbanteCart Error logs:

AMail. transport: Symfony\Component\Mailer\Transport\SendmailTransport: Unable to write bytes on the wire.

Can you PM me a credentials to your cPanel ?

Can The 'Buy It Now' Button Be Disabled?

 

Setting added into new version of FC inside developer branch 1.3.3.
You got it after upgrade. Or you can replace your folder extensions/fast_checkout with folder from current dev branch

For instance when an order is placed, I do get notified automatically by email. However, when I attempt to view the message using Windows default mail app, it keeps loading endlessly without displaying anything. I've also tried viewing the message directly on my browser by logging into my email account. Interestingly, it shows on the browser, but in an unreadable format, as shown on the screenshot attached. Kindly advise.

is this issue still actual?