Hello Emanuel,
The first step would be to make sure your application is listening for requests on the port 443.
Once that is done, you need to make sure the firewall is allowing the requests to actually reach the post 443.
You can create a rule via the Cloud Console with these instructions [1]. Here is an example of how to create a rule via the Cloud Shell [2].
If you are using this command [2], make sure you assign the tag “webserver" to your node [3] so the firewall rule applies to it.
Regards,
Frederic
[1] https://cloud.google.com/vpc/docs/using-firewalls#creating_firewall_rules
[3] https://cloud.google.com/vpc/docs/add-remove-network-tags#adding_and_removing_tags