Check your system to see if the requirements are met
https://abantecart.atlassian.net/wiki/spaces/AD/pages/3768390/AbanteCart+System+Requirements

Seeing any errors in your admin error log?
I see there are several extensions included in the Mercato -  perhaps try turning one off at time  until you find the problem?
Then I would try the developer again. 

Have you installed the extension version that is correct for the cart version you are using??
here is the link to the product in Market Place

https://marketplace.abantecart.com/lightbox_html5

Also,  are you sure that your minor changes haven't caused a conflict? We have this in use on several sites and have no issues with it.

it is a Language Definitions

see screen shot for the where and how
you can edit directly in the field on the grid,  OR  open the edit

those of you who want more function in the blurb might find this extension adds a lot more options,  and you don't have to remember from version upgrade what CSS you changed.

https://marketplace.abantecart.com/editor

or see our manual for all features here

https://why2central.net/docs/editor-1215-overview/

Above the description box in each product page,  there is another small box  labeled BLURB.   Try adding your descriptor in there

there is a known issue with authorize net for v 1.3.3 

The core devs have fixed it for the next release.   In the meantime you can find the patch file here
https://why2central.net/patch/abantecart-v1-3-3-default-authorizenet-patch-file/

along with the directions of how to install it.

This should get your issue resolved.

The support team at WHY2

Hello,  we have submitted to the core devs a solution for this.   They have accepted our solution and merged it into the core files for the next AbanteCart v 1.3.4 when it is released in the future.

In the meantime we have posted the files changes to our WHY2 info center -  along with complete instructions on how to download and install them.  This should only be applied to AbanteCart v 1.3.3
https://why2central.net/patch/abantecart-v1-3-3-min-and-max-order-subtotal-threshold-for-shippers-patch-files/

This link if from our soon to be released How2 info site -  it is NOT currently released publicly,  but will be soon.

https://how2.why2central.net/knowledgebase/hide-shipper-from-being-shown-to-customer/

Let us know how it works out for you.

Regards,
The support team from WHY2

Yes,  i understood previously  that you installed manually. 

BUT,  if you have cPanel and Softaculous  you can import your current installation into Softaculous for better management.   It is NOT a new installation,  it is an import of the existing installation.  Nothing will change, in your current installation.  It just allows you to do more things, with less hassle.

If you have Softaculous in your cPanel,  this will add the ability to change your admin password  which is your current issue.   It will also add the ability to clone or stage your existing site to test what is any issue you may have in updating your cart version or just testing out something new  -  all WITHOUT impacting your existing site.