Unable to open COD -> Manage

Hi,

Woocommerce -> Version 4.0.1
WordPress -> 5.4.1
Woo SmartCOD -> Version 1.4.9.6

Issue:
Not able to open the COD -> Manage button as it shows “Try:

Checking the connection
Checking the proxy and the firewall
ERR_CONNECTION_CLOSED”

History: The plugin was working well. I had put an extra fee for COD using this plugin and the site was live. After that, when i try to open the COD -> Manage button, it started throwing Fatal Error -> Fatal error: Maximum execution time of 30 seconds exceeded. Since, i had to open COD and make modifications, I tried to increase the time in server. But it didn’t work. So, I uninstalled this plugin.

Once Uninstalled, the COD-> Mange button started working.

Now, when I re-installed I am not able to open the COD -> Manage button as it shows “Try:

Checking the connection
Checking the proxy and the firewall
ERR_CONNECTION_CLOSED”

Would appreciate if you could look into this.
Note: There are no other COD plugins being used.