I am able to generate the access token using POST command as mentioned in this document.
Attached sample commands syntax tested at my side.
POST https://management.azure.com/subscriptions/b04775c3-63fa-40f3-9430-139d2e5522d3/resourceGroups/contosto-videoanalyzer-rg/providers/Microsoft.VideoIndexer/accounts/contosto-videoanalyzer/generateAccessToken?api-version=2024-01-01
{
"permissionType": "Contributor",
"scope": "Account"
}
Please upvote my answer if it helps.
Thank you.