Hi Volga,
Your client registration facility is disabled at your Gluu CE side. You need to enable it in order to create dynamic client.
To enable this feature in oxTrust(Gluu CE GUI), navigate to `Configuration > JSON Configuration > oxAuth configuration`, and find the `dynamicRegistrationEnabled` property. Set it to true to enable dynamic client registration.
For more info, please check Gluu CE docs here https://gluu.org/docs/ce/4.0/admin-guide/openid-connect/#dynamic-client-registration
Thanks,
Meghna