Calling a Teams Bot Framework App from ACS?

Question

We have a Teams bot that can handle calls and chat. Additionally via resource accounts we have assigned a SIP address as well as a PSTN Number to this bot.

We have created an ACS resource and added it as a Channel to the Teams Bot. This assigns an 8:acs: ID to the bot for use with ACS.

Now we wish to CALL the Teams Bot (not chat) from ACS. The user on the ACS end is not a Teams/Entra user.

When using the sample Calling Apps for ACS, this call fails with error

Call end reason: code: 480, subcode: 10077

(The sample ACS Calling app is able to connect to an existing MS Teams Meeting in the same UI so the overall set up etc is correct. See app screen shot below)

Questions

1. Is this a supported scenario? I see docs that suggest ACS can call a Call Queue or Auto Attendant. However this is a straight bot framework bot with working call settings.
2. If supported, what ID should be used to call the Teams bot from ACS. (We have tried with the Bot Service issued Channel ID
3. If the ACS ID used is correct, what does the error code indicate? Call end reason: code: 480, subcode: 10077 (Quick search shows this indicates that a user was not online, but here the end point is a Teams bot, so always connected and online)