"We can't setup the conversation because your organizations are not setup to talk to each other"

[Joe McGowan]

I get this message when I try to Teams chat with another tenant.  Do both tenants have to be in "Teams Only" mode at the org level for this to work?  Tenant A is in Islands Mode with external access enabled, Tenant B is in Teams only mode with external access enabled.  Chat message is being initiated from Tenant A.

Thanks!

[#2]

@Joe McGowan 

The PowerShell cmdlets mentioned here were certainly helpful (using the Microsoft Teams PowerShell module --not the Skype for Business PowerShell module--)

I fixed this by adding the domain to the allowed list of domains in the Teams Admin center then waited for 10-15 minutes. I was now able to collaborate with users outside our tenant.