This article will help you grant Full Access permissions to your service account for your resources in Microsoft 365. This step is necessary for successful integration.
Prerequisites:
The service account is created. If not, check the article on how to create a service account.
Log in to your admin account and go to the Exchange admin center at https://admin.exchange.microsoft.com/.
Click on Recipients.
Click on Resources.
Select your resource.
Click on Delegation.
In Read and manage (Full Access) section click on Edit.
Click on Add members.
Select your service account.
Click Save.
After the confirmation it usually takes 5 minutes to effect the changes and no longer than 30 minutes. According to Microsoft Documentation it can occasionally take up to 24 hours.