twilio_phone_number.sms.primary_url not implemented

I'm running Terraform 0.12.8 with terraform-provider-twilio built with #19 . I added a new phone number to my config and applied it. Twilio shows the new number but it never got the SMS webhook URL configured.

I changed the webhook URL value and terraform apply fails:

module.test_helper.twilio_phone_number.number: Modifying... [id=nnnnnnn]

Error: Not implemented

Here is the config, with irrelevant parts removed or redacted:

$ terraform version
Terraform v0.12.8
...
+ provider.twilio (unversioned)
$ terraform show
...
# module.test_helper.twilio_phone_number.number:
resource "twilio_phone_number" "number" {
    country_code  = "US"
    friendly_name = "com-company-dev-phone-number"
    id            = "nnnnnnnnnnnnn"
    number        = "+1415nnnnnnn"
    search        = "415"

    sms {
        primary_http_method = "POST"
        primary_url         = "http://com-company-dev-phone-number-eb-env.nnnnn.us-west-1.elasticbeanstalk.com/twilio_webhook"
    }
}
$ cat main.tf 
...
resource "twilio_phone_number" "number" {
  friendly_name = "${var.instance_name}-phone-number"
  country_code  = "US"
  search        = "415"
  sms {
    primary_url         = "http://${aws_elastic_beanstalk_environment.default.cname}/twilio_webhook"
    primary_http_method = "POST"
  }
}

output "phone_number" {
  value = "${twilio_phone_number.number.number}"
}
$ terraform plan
Refreshing Terraform state in-memory prior to plan...
The refreshed state will be used to calculate this plan, but will not be
persisted to local or remote state storage.

...
module.test_helper.twilio_phone_number.number: Refreshing state... [id=nnnnnnnnnn]

------------------------------------------------------------------------

No changes. Infrastructure is up-to-date.

This means that Terraform did not detect any differences between your
configuration and real physical resources that exist. As a result, no
actions need to be performed.

Preskton / terraform-provider-twilio

twilio_phone_number.sms.primary_url not implemented #20