Can't create transient document with group permissions

Previously, I had created an OAuth token with permissions to read, write, and send agreements for myself and I was able to complete the workflow through creating transient documents, creating and sending an agreement to be signed, checking the agreement status, and signing the agreement and sending completed documents to the signers.

Now I've created an app with permissions to read, write, and send agreements for the group. I am a group admin, so that shouldn't be the issue. I'm able to create a token that's ostensibly compatible with these permissions. But when I submit to /api/rest/v6/transientDocuments using a dummy file and the Bearer token I received I get the following response:

{
    "code": "PERMISSION_DENIED",
    "message": "The API caller does not have the permission to execute this operation"
}

Why am I not able to create a transient document using the token I generated with an account that has the appropriate permissions?

If I add an x-api-user header with email:<my email address> as the value, I get the same error, so it's apparently not that it needs further identifying information.

Is there a permission I need to set besides agreement_read:group, agreement_write:group, and agreement_send:group?