Bamboo Specs bamboo.yaml does not like include Edited

[BX]

bamboo.yaml:

---
version: 2
!include 'PlanName/spec.yml'

I have also tried moving 'spec.yml' to the same directory:

---
version: 2
!include 'spec.yml'

Both scenarios give me:

Bamboo YAML import failed: Invalid format of the YAML file: while scanning a simple key in 'reader', ... !include 'PlanName/spec.yml'
                                                                                                         ^
could not find expected ':' in 'reader' ... 'PlanName/spec.yml'
                                                                  ^

(The carats didn't format properly, but the first one is under the exclamation point of "!include 'PlanName/spec.yml'", and the second carat is underneath the end of ".../spec.yml'")

The documentation shows that what I am doing is the correct way to implement the '!include' statement in the 'bamboo.yaml' file:

Using your main YAML file to include every other plan

# bamboo.yaml
---
!include 'planA.yaml'
---
!include 'planB.yaml'


# planA.yaml
---
version: 2
# ...


# planB.yaml
---
version: 2
# ...

Why isn't this working?