R - Arguments for Graph API notifications subscription: error HTTP 405 - r

Question

I'm trying to create a subscription to the callRecords notifications with Graph API in R. I'm looking at this Microsoft page as a reference: https://learn.microsoft.com/en-us/graph/api/subscription-post-subscriptions?view=graph-rest-beta&tabs=http
Here is my code:
Subscribtion_Call <- AzureGraph::call_graph_endpoint(Tok, options = list(), api_version = Version, operation = "subscriptions", content_type = "application/json")
Subscription_Properties <- list(
changeType = "created,updated",
notificationUrl = "https://webhook.azurewebsites.net/notificationClient",
resource = "communications/callRecords",
expirationDateTime = "2022-04-09T11:00:00.0000000Z",
clientState = "SecretClientState"
)
Send_Subscription <- call_graph_url(Tok, Endpoint, body = Subscription_Properties, encode = "json",
content_type = "application/json",
http_verb = "POST",
http_status_handler = "message",
simplify = FALSE,
auto_refresh = TRUE
)
This gets me an HTTP 405 error as below:
> Subscribtion_Call <- AzureGraph::call_graph_endpoint(Tok, options = list(), api_version = Version, operation = "subscriptions", content_type = "application/json")
>
> Subscription_Properties <- list(
+ changeType = "created,updated",
+ notificationUrl = "https://webhook.azurewebsites.net/notificationClient",
+ resource = "communications/callRecords",
+ expirationDateTime = "2022-04-09T11:00:00.0000000Z",
+ clientState = "SecretClientState"
+ )
>
> Send_Subscription <- call_graph_url(Tok, Endpoint, body = Subscription_Properties, encode = "json",
+ content_type = "application/json",
+ http_verb = "POST",
+ http_status_handler = "message",
+ simplify = FALSE,
+ auto_refresh = TRUE
+ )
Method Not Allowed (HTTP 405). Failed to complete operation. Message:
.
If I change the http_verb to "GET" this is returned:
> Send_Subscription <- call_graph_url(Tok, Endpoint, body = Subscription_Properties, encode = "json",
+ content_type = "application/json",
+ http_verb = "GET",
+ http_status_handler = "message",
+ simplify = FALSE,
+ auto_refresh = TRUE
+ )
OK (HTTP 200). Failed to complete operation. Message:
.
>
What am I missing?
Thanks in advance for your help!