Leapp Upgrade from RHEL 7.7 to RHEL 8

I am trying to upgrade my system from RHEL 7.7 to RHEL 8 as per the instructions provided in Upgrading to RHEL 8

However I am encountering following error :

# leapp preupgrade
Loaded plugins: langpacks, product-id, subscription-manager
============================================================
                           ERRORS                           
============================================================

2019-08-19 15:00:24.363331 [ERROR] Actor: target_userspace_creator Message: A subscription-manager command failed to execute
Detail: {u'hint': u'Please ensure you have a valid RHEL subscription and your network is up.'}

============================================================
                       END OF ERRORS                        
============================================================

============================================================
                           REPORT                           
============================================================

A report has been generated at /var/log/leapp/leapp-report.txt

A report has been generated at /var/log/leapp/leapp-report.json

============================================================
                       END OF REPORT                        
============================================================

I do have a valid RedHat Developer Valid subscription :

# subscription-manager list
+-------------------------------------------+
    Installed Product Status
+-------------------------------------------+
Product Name:   Red Hat Enterprise Linux Server
Product ID:     69
Version:        7.7
Arch:           x86_64
Status:         Subscribed
Status Details: 
Starts:         11/29/2018
Ends:           11/29/2019

# subscription-manager release
Release: 7.7

Could you please help me figure out the error with the upgrade and solution to it

Regards,

LuckyDudeThakur

https://twitter.com/@LuckyDudeThakur
https://www.linkedin.com/in/luckydudethakur