Hi @Dom Lowry
Only the users who are owners or members of the shared channel can access the channel. While guests (people with Microsoft Entra guest accounts in your organization.) can't be added to a shared channel, you can invite people outside your organization to participate in a shared channel by using Microsoft Entra B2B direct connect.
Have you enabled external access? If not, you need enable external access firstly:
- In the Teams admin center, expand Users, and then select External access.
- Under Teams and Skype for Business users in external organizations, ensure that the organizations that you want to collaborate with are not blocked.
And then configure shared channels:
- In the Teams admin center, expand Teams, and then select Teams policies.
- Select the policy for which you want to enable shared channels, and then select Edit.
- To allow users to be invited to shared channels in other organizations, turn Join external shared channels on.
- Select Apply.
For users to invite people from outside your organization to a shared channel, both organizations must set up an organizational relationship in Microsoft Entra B2B direct connect. You can specify an internal link for users who try to share a channel with people in an organization where a two-way Microsoft Entra B2B direct connect relationship has not been set up. This link appears when they try to share the channel. Use this link to direct your users to your internal support page or request form for setting up shared channels with other organizations.
To specify an internal help link for shared channel users
- In the Teams admin center, expand Teams, and then select Teams settings.
- Under Shared channels, turn Provide a link to my support request page on.
- Type the URL to your support page in the Support request page link box.
- Select Save.
For more details, you may refer to the article.
Hope the information is helpful for you!
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