AWS Cloudformation - security group ids list export and import - SecurityGroupIds not valid - aws-cloudformation

Question

Im working with 2 nested stacks. I need to use security group ids exported from NestedA in NestedB. The exported security group ids are to be used in a SecurityGroupIds property in NestedB based on conditions.
However cloudformation returns error: Property validation failure: [Value of property {/LaunchTemplateData/SecurityGroupIds/0} does not match type {String}]
The following are snippets of what I have tried:
NestedA export
Outputs:
SG1
Value: !Join
- ','
- - !Ref securitygroup1
- !Ref securitygroup2
Export:
Name: !Sub ${ExportVpcStackName}-SG1
SG2
Value: !Join
- ','
- - !Ref securitygroup3
- !Ref securitygroup4
Export:
Name: !Sub ${ExportVpcStackName}-SG2
ParentStack
Resources:
...
launchtemplate:
Type: AWS::Cloudformation::Stack
Properties:
TemplateURL: https://s3/nestedB.yaml
...
SG1:
Fn::ImportValue: !Sub ${ExportVpcStackName}-SG1
SG2:
Fn::ImportValue: !Sub ${ExportVpcStackName}-SG2
NestedB import
Parameters:
SG1
Type: List<AWS::EC2::SecurityGroup::Id>
SG2
Type: List<AWS::EC2::SecurityGroup::Id>
Resources:
launchtemplate:
Type: AWS::EC2::LaunchTemplate
Properties:
LaunchTemplateData:
...
SecurityGroupIds:
!If
- Condition1
-
- !Ref SG1
- !Ref SG2
- !If
- Condition2
-
- !Ref SG1
- !Ref AWS::NoValue
Ive also tried importing each of the security groups directly/individually into NestedB with no success ie:
NestedA export
Outputs:
securitygroup1:
Value: !Ref securitygroup1
Export:
Name: !Sub ${ExportVpcStackName}-securitygroup1
securitygroup2:
Value: !Ref securitygroup2
Export:
Name: !Sub ${ExportVpcStackName}-securitygroup2
securitygroup3:
Value: !Ref securitygroup3
Export:
Name: !Sub ${ExportVpcStackName}-securitygroup3
securitygroup4:
Value: !Ref securitygroup4
Export:
Name: !Sub ${ExportVpcStackName}-securitygroup4
NestedB import
Resources:
launchtemplate:
Type: AWS::EC2::LaunchTemplate
Properties:
LaunchTemplateData:
...
SecurityGroupIds:
!If
- Condition1
-
- Fn::ImportValue: !Sub ${ExportVpcStackName}-securitygroup1
- Fn::ImportValue: !Sub ${ExportVpcStackName}-securitygroup2
- Fn::ImportValue: !Sub ${ExportVpcStackName}-securitygroup3
- Fn::ImportValue: !Sub ${ExportVpcStackName}-securitygroup4
- !If
- Condition2
-
- Fn::ImportValue: !Sub ${ExportVpcStackName}-securitygroup1
- Fn::ImportValue: !Sub ${ExportVpcStackName}-securitygroup2
- !Ref AWS::NoValue
Whats the error Im making?
Edit: I have tried #marcin suggestion but still get the error:
Property validation failure: [Value of property {/LaunchTemplateData/SecurityGroupIds/0} does not match type {String}]

Answer 1

Instead of Type: List<AWS::EC2::SecurityGroup::Id>, please use CommaDelimitedList.
Also your SG1 is a list of SGs. You have to use Fn::Select to get individual SG values from the list.