You mean this one :
0_1551371049246_4a228a85-d762-41e8-8242-d5669f041918-image.png
Did it showed available packages in the past ?
It never showed any packages ?
Have a look at your :
0_1551371175064_896fba38-6eda-48cd-b35e-5eb9dbbbc225-image.png
You see the "Version information updated at Thu Feb 28 15:45:56 CET 2019" ?
What is your date / time ?
The question that takes care of 75 % of all "can't upgrade/update/install packages" cases : you broke the DNS, so pfSense itself can't reach out to the Internet anymore.
Repair or undo your DNS settings - go back to the "always works" mode : the one that was present by default.
If not, you are lined up for the conquest : "Asking a question without any useful information" 👍