The Catalog Repository for 1.2.8 is "dnac12y"
SSH to the Cisco DNA Center or use the CIMC KVM Console:
$ ssh maglev@dnac.ip.address -p 2222
$ maglev login
$ maglev catalog settings display
$ magctl service setenv catalogserver PARENT_CATALOG_SERVER_REPOSITORY dnac12y
Note: Once the catalog repository is changed, the catalog service will restart. Wait for up to 5 minutes to allow the necessary services to come back up. You can monitor by watching the amber bar in the UI (needs to disappear) or run the following CLI command:
$ watch -d -n 0.5 "magctl appstack status | egrep 0/"
Once the Catalog Service is up and running...
$ maglev catalog settings display
$ maglev catalog settings validate
$ maglev catalog check_for_updates
Then go back to browser and go to Software Updates. Click Refresh on the Browser 3-5 times to clear the browser cache. You should see the screens that were there prior to selecting "Switch Now"
If you continue to have issues, Please open a Cisco TAC Case and the Cisco DNA Engineer can assist you in fixing the issues.
Regards
T.