Self-service accounts (under the Pro plan) can upgrade and downgrade by themselves via the account’s settings.
Possible reasons why the account is not eligible for a downgrade:
- Exceeding plan limits of lower plan
- Outstanding balance
- Multiple Users - enabled from Plus plan
- Sub Accounts - enabled from Plus plan
- CNAME - enabled from Advanced plan
- Other account restrictions - please contact us via this form: https://support.cloudinary.com/hc/en-us/requests/new