Unable to store terraform data in Manta

[dekobon]

When using the go-cli, I can't store my terraform data in Manta:

$ ./triton-kubernetes create manager
✔ Backend Provider: Manta
✔ Triton Account Name (usually your email): <redacted>
✔ Triton Key Path: ~/.ssh/id_rsa
✔ Triton URL: https://us-east-1.api.joyent.com
create manager called
✔ Cluster Manager Name: demo-1
✔ Highly Available: Yes
✔ How many master nodes: 2
✔ Triton Account Name (usually your email): <redacted>
✔ Triton Key Path: ~/.ssh/id_rsa
✔ Triton URL: https://us-east-1.api.joyent.com
✔ Triton Networks: Joyent-SDC-Public
  Attach another? No
✔ Triton Image: ubuntu-certified-16.04@20180109
✔ Triton SSH User: root
✔ Rancher Master Triton Machine Package: k4-highcpu-kvm-3.75G
Downloading modules...
Get: git::https://github.com/joyent/triton-kubernetes.git?ref=go-cli

Initializing the backend...

Error configuring the backend "manta": Failed to configure remote backend "manta": Error getting Manta credentials: Error constructing authentication for <redacted>: invalid private key data:

Please update the configuration in your Terraform files to fix this error
then run this command again.

exit status 1

[dekobon]

The problem may be that the installer prompts for:

Triton URL: https://us-east-1.api.joyent.com

instead of a Manta URL.