Hi @SK · Welcome to Q&A platform and thanks for your query.
I just tested running above call in my tenant and got the lastSignInDateTime in response as you can see below:
Could you please confirm you have consented for below permissions and if you decode your access token at https://jwt.ms below permissions are present in SCP claim:
- AuditLogs.Read.All
- Organisation.Read.All
Also, the lastSignInDateTime property is a new feature, the value of the lastSignInDateTime property can be blank if:
- The last successful sign-in of a user took place before April 2020.
- The affected user account was never used for a successful sign-in.
Read more:
- https://learn.microsoft.com/en-us/azure/active-directory/reports-monitoring/howto-manage-inactive-user-accounts
- https://learn.microsoft.com/en-us/graph/api/resources/signinactivity?view=graph-rest-beta
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