C4 diagram not possible to create relation from boundaries to container

[Volland]

Description

C4 diagram not possible to create relation from boundaries to container

C4Container
    title Container diagram for Internet Banking System

    System_Ext(email_system, "E-Mail System", "The internal Microsoft Exchange system", $tags="v1.0")
    Person(customer, Customer, "A customer of the bank, with personal bank accounts", $tags="v1.0")

    Container_Boundary(c1, "Internet Banking") {
        Container(spa, "Single-Page App", "JavaScript, Angular", "Provides all the Internet banking functionality to cutomers via their web browser")
        Container_Ext(mobile_app, "Mobile App", "C#, Xamarin", "Provides a limited subset of the Internet banking functionality to customers via their mobile device")
        Container(web_app, "Web Application", "Java, Spring MVC", "Delivers the static content and the Internet banking SPA")
        ContainerDb(database, "Database", "SQL Database", "Stores user registration information, hashed auth credentials, access logs, etc.")
        ContainerDb_Ext(backend_api, "API Application", "Java, Docker Container", "Provides Internet banking functionality via API")

    }
    Rel(c1, email_system, 'aa')
    System_Ext(banking_system, "Mainframe Banking System", "Stores all of the core banking information about customers, accounts, transactions, etc.")

Steps to reproduce

Try to create relation on C4 diagram that use boundaries

C4Container
    title Container diagram for Internet Banking System

    System_Ext(email_system, "E-Mail System", "The internal Microsoft Exchange system", $tags="v1.0")
    Person(customer, Customer, "A customer of the bank, with personal bank accounts", $tags="v1.0")

    Container_Boundary(c1, "Internet Banking") {
        Container(spa, "Single-Page App", "JavaScript, Angular", "Provides all the Internet banking functionality to cutomers via their web browser")
        Container_Ext(mobile_app, "Mobile App", "C#, Xamarin", "Provides a limited subset of the Internet banking functionality to customers via their mobile device")
        Container(web_app, "Web Application", "Java, Spring MVC", "Delivers the static content and the Internet banking SPA")
        ContainerDb(database, "Database", "SQL Database", "Stores user registration information, hashed auth credentials, access logs, etc.")
        ContainerDb_Ext(backend_api, "API Application", "Java, Docker Container", "Provides Internet banking functionality via API")

    }
    Rel(c1, email_system, 'aa')
    System_Ext(banking_system, "Mainframe Banking System", "Stores all of the core banking information about customers, accounts, transactions, etc.")

Screenshots

No response

Code Sample

C4Container
    title Container diagram for Internet Banking System

    System_Ext(email_system, "E-Mail System", "The internal Microsoft Exchange system", $tags="v1.0")
    Person(customer, Customer, "A customer of the bank, with personal bank accounts", $tags="v1.0")

    Container_Boundary(c1, "Internet Banking") {
        Container(spa, "Single-Page App", "JavaScript, Angular", "Provides all the Internet banking functionality to cutomers via their web browser")
        Container_Ext(mobile_app, "Mobile App", "C#, Xamarin", "Provides a limited subset of the Internet banking functionality to customers via their mobile device")
        Container(web_app, "Web Application", "Java, Spring MVC", "Delivers the static content and the Internet banking SPA")
        ContainerDb(database, "Database", "SQL Database", "Stores user registration information, hashed auth credentials, access logs, etc.")
        ContainerDb_Ext(backend_api, "API Application", "Java, Docker Container", "Provides Internet banking functionality via API")

    }
    Rel(c1, email_system, 'aa')
    System_Ext(banking_system, "Mainframe Banking System", "Stores all of the core banking information about customers, accounts, transactions, etc.")

### Setup

- Mermaid version: 10.4.0
- Browser and Version: Chrome
Same for VScode extension

### Suggested Solutions

_No response_

### Additional Context

_No response_