Cannot set AWS Cognito Email/SMS templates using parameters

[jacob-swanson]

I'm having an issue where part of my string parameter is getting erased by Sceptre.
The value in question is {####}, which is used by AWS Cognito as a template placeholder.
When this value is passed as a parameter in Sceptre, it's removed.

Config snippet:

template_path: cognito/pool.yaml
parameters:
  ...
  InviteEmailTemplate: >
    Welcome, click this link to confirm your account:
    https://example.com/confirm?username={username}&confirmationCode={####}

Template snippet:

Parameters:
  InviteEmailTemplate:
    Description: Template for user invite email.
    Type: String
...
Resources:
  UserPool:
    Type: AWS::Cognito::UserPool
    Properties:
      ...
      AdminCreateUserConfig:
        InviteMessageTemplate:
          EmailMessage: !Ref InviteEmailTemplate
...

The value that is sent to CloudFormation is:

Welcome, click this link to confirm your account:
https://example.com/confirm?username={username}&confirmationCode=

Which fails due to it missing {####} with the following error:

 Member must satisfy regular expression pattern: [\p{L}\p{M}\p{S}\p{N}\p{P}\s*]*\{####\}[\p{L}\p{M}\p{S}\p{N}\p{P}\s*]*

[nathan-williams-rozettatechnology]

Try wrapping the line in a raw block: https://jinja.palletsprojects.com/en/2.11.x/templates/#escaping
Something like:

template_path: cognito/pool.yaml
parameters:
  ...
  InviteEmailTemplate: >
    Welcome, click this link to confirm your account:
{% raw %}
    https://example.com/confirm?username={username}&confirmationCode={####}
{% endraw %}

[ngfgrant]

@jacob-swanson did @nathan-williams-rozettatechnology suggestion help?