Terraform Load-Balancer Pool Creation Fails

I am trying to create Traffic load-balancer/-pools with Terraform, passing email/api-key to provider since api-tokens are not supported by provider. However, creation fails calling for a support request:

│ Error: error creating load balancer pool: HTTP status 400: Internal error creating or modifying pool. Access Failed. Please reach out to Support.: validation failed (1002)

│ with cloudflare_load_balancer_pool.endpoint[“foobar”],
│ on main.tf line 11, in resource “cloudflare_load_balancer_pool” “endpoint”:
│ 11: resource “cloudflare_load_balancer_pool” “endpoint” {

Following up on my own question:
In our case, also setting the account_id argument on the provider solved it for us.