App Transfer auth/usermigrationinfo access_denied

I'm facing the following issue when I try to use the API https://appleid.apple.com/auth/usermigrationinfo

I am currently preparing for app migration and planning to use auth/usermigrationinfo to generate a transfer identifier.

My request parameters are as follows.

sub=( team-scoped user identifier)
target=(Team ID Target 10 letters)
client_id=Bundle id
client_secret= Secret generated with private key

However, after calling the API, I received the following error response.

{
    "error": "access_denied"
}

Does this API call have a time limit, and must it be called only after the app migration is completed?

Thanks & regards