AD failing after validating all permissions and communications

I have integrated an AD asset to manage accounts.

When I read users or groups it works perfectly

1. I can discover accounts in the AD

2. I can test the asset successfully

3. I can test connection sucessfully

4. I can check the functional account successfully

5. I can sync the AD with no errors

but when I try to change another password fail with the following message:
Debug ChangePassword failed. Access to the resource was denied. (PrincipalOperationException) HResult: 0x80131501

(the service-functional account is domain admin of the domain)
 

We have followed step by step that the follwoing article says:

https://support.oneidentity.com/es-es/one-identity-safeguard-for-privileged-passwords/kb/4263587/how-to-delegate-permissions-in-active-directory-for-a-safeguard-service-account-4263587?kblang=en-US

 Some help please?