Teams Export API not allowing me to filter by channel - microsoft-graph-api

Question

I'm trying to use the Teams Export API to export a single Teams channel. I have my permissions set up properly; if I make a request to
https://graph.microsoft.com/v1.0/teams/{TEAM_ID}/channels/getAllMessages (without specifying a filter), I get the paginated results of all of the channel messages on my team. If I copy the sample datetime filters in that documentation, I also get a successful response with the appropriate results.
A successful response gives me a list of messages. Each one shows a channelIdentity field, which contains a channelId (fields removed for readability):
{
"value": [
{
"channelIdentity": {
"teamId": "{TEAM ID}",
"channelId": "{CHANNEL ID}"
},
},
]
}
What I want is to use this channelIdentity/channelId field as a filter on the results, so that I can export just the messages from a single channel.
If I run GET https://graph.microsoft.com/v1.0/teams/{TEAM_ID}/channels/getAllMessages?$filter=channelIdentity/channelId eq '{CHANNEL ID}', I get an error:
{
"error": {
"code": "BadRequest",
"message": "The entity property 'channelIdentity/channelId' and operationKind 'Equal' is not allowed in $filter query.",
"innerError": {
"date": "2022-11-16T23:47:06",
"request-id": "...",
"client-request-id": "..."
}
}
}
This reads to me like I'm not allowed to use eq with this ID. If I try a 'starts with', I get a different error:
GET https://graph.microsoft.com/v1.0/teams/{TEAM_ID}/channels/getAllMessages?$filter=startswith(channelIdentity/teamId, '{CHANNEL ID}')
{
"error": {
"code": "BadRequest",
"message": "Only binary operation expressions are allowed.",
"innerError": {
"date": "2022-11-17T00:11:26",
"request-id": "...",
"client-request-id": "..."
}
}
}
I'm unclear on what this is trying to say - either the ID starts with that phrase or it doesn't; it seems like a binary expression to me.
Is there some other approach I should use to get these results filtered by channel ID?

Answer 1

This API is designed to export everything from a team for backup/archival scenario. So, filtering by a specific channel is not supported now.
If you wish you may suggest this feature on Microsoft Feedback portal.

Answer 2

Any reason why you don't use List Channel Messages?
You can then make a GET call against this URL:
"https://graph.microsoft.com/v1.0/teams/{teamid}/channels/{channel id}/messages"
Note - as per that link you will need to Request access:
https://learn.microsoft.com/en-us/graph/teams-protected-apis
One other method, if you are using Graph Explorer, is add the signed-in user to the team as an owner, and it will let you test this method, you just won't be able to call via an App Registration until you do fill out that form.