Hello,
It looks like the issue occurs because the account that was specified during the domain registration in Adaxes does not have required permissions in Exchange. For information on how to check/change the account, have a look at the following help article: https://www.adaxes.com/help/ChangeManagedDomainServiceAccount. It is recommended to assign the account to the Organization Management role group. It provides administrative access to an entire Exchange organization and can perform almost any task.
If, for some reason, you do not want to provide the account administrative access to your Exchange organization, you need to assign the account to the following role groups in Exchange:
For more details, see Understanding Management Roles.