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That error indicates the command you actually ran was slightly different. Something like this:

set group name "Geo-Block" members.add.1 "Albania1"

After running this:

[Expert@DallasSA]# mgmt_cli -f json -r true update-updatable-objects-repository-content
...
[Expert@DallasSA]# mgmt_cli -f json -r true show updatable-objects-repository-content details-level full limit 500 offset 0 | jq -c '.objects[]|.' >> updatable.json
[Expert@DallasSA]# mgmt_cli -f json -r true show updatable-objects-repository-content details-level full limit 500 offset 500 | jq -c '.objects[]|.' >> updatable.json
[Expert@DallasSA]# mgmt_cli -f json -r true show updatable-objects-repository-content details-level full limit 500 offset 1000 | jq -c '.objects[]|.' >> updatable.json
[Expert@DallasSA]# mgmt_cli -f json -r true show updatable-objects-repository-content details-level full limit 500 offset 1500 | jq -c '.objects[]|.' >> updatable.json
[Expert@DallasSA]# mgmt_cli -f json -r true show updatable-objects-repository-content details-level full limit 500 offset 2000 | jq -c '.objects[]|.' >> updatable.json
[Expert@DallasSA]# mgmt_cli -f json -r true show updatable-objects-repository-content details-level full limit 500 offset 2500 | jq -c '.objects[]|.' >> updatable.json
[Expert@DallasSA]# mgmt_cli -f json -r true show updatable-objects-repository-content details-level full limit 500 offset 3000 | jq -c '.objects[]|.' >> updatable.json
[Expert@DallasSA]# mgmt_cli -f json -r true show updatable-objects-repository-content details-level full limit 500 offset 3500 | jq -c '.objects[]|.' >> updatable.json
[Expert@DallasSA]# mgmt_cli -f json -r true show updatable-objects-repository-content details-level full limit 500 offset 4000 | jq -c '.objects[]|.' >> updatable.json
[Expert@DallasSA]# wc -l updatable.json 
4249 updatable.json
[Expert@DallasSA]# grep "GEO Locations" updatable.json | jq '."name-in-updatable-objects-repository"' | sort
"Afghanistan"
"Africa"
"Aland Islands"
"Albania"
"Algeria"
"American Samoa"
"Andorra"
"Angola"
"Anguilla"
"Antarctica Other"
"Antarctica"
...

you can see all of the country object names. Each country object must be imported via 'mgmt_cli ... add updatable-object uid-in-updatable-objects-repository <UUID>' before you can actually use it. Once imported, the names will be as above.