Forticare response error 61 when trying to register permanent test license

I am trying to register a permanent test licence for a fortigate - I did this once, but am unable to do it a second time.

I know that only one licence is available per Forticare account, but I have decommissioned the previous licence in the Assets screen.

When I try to register the licence it does not reboot the Fortigate VM.   When I debug what happens, I see this:

[httpsd 4215 - 1730202905     info] fweb_debug_init[605] -- User-Agent: "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/129.0.0.0 Safari/537.36" [httpsd 4215 - 1730202905     info] fweb_debug_init[607] -- Handler "api_monitor_v2-handler" assigned to request [httpsd 4215 - 1730202905     info] is_vm_uri[1144] -- allowing VM URI '/api/v2/monitor/system/vmlicense' [httpsd 4215 - 1730202905     info] api_store_parameter[308] -- add API parameter 'vdom' (type=string) [httpsd 4215 - 1730202905     info] api_store_parameter[308] -- add API parameter 'account_id' (type=string) [httpsd 4215 - 1730202905     info] api_store_parameter[308] -- add API parameter 'account_password' (type=string) [httpsd 4215 - 1730202905     info] api_store_parameter[308] -- add API parameter 'is_government' (type=boolean) [httpsd 4215 - 1730202905     info] endpoint_process_req_vdom[1067] -- new API request (action='download-eval',path='system',name='vmlicense',vdom='root',user='admin') Requesting FortiCare Trial license, proxy:(null) Forticare response error 61. [httpsd 4215 - 1730202908    error] system_vmlicense_download_eval[303] -- Failed to download VM license (error = 61). [httpsd 4215 - 1730202908    error] api_return_http_result[1272] -- API error 500 raised [httpsd 4215 - 1730202908     info] endpoint_process_req_vdom[1073] -- completed API request (rss_pre=52112, rss_post=52124, rss_delta=12)

As you can see, i don't have any assets registered to my account.   The Fortigate is able to ping internet hosts by name, so this is not a name resolution or reachability problem - in fact you can see from the out put above, it is successfully getting a response from the API.  Just not the one I need.

Any help appreciated!

Andrew