@Gökhan Demirci , I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this! Since the Microsoft Q&A community has a policy that the question author cannot accept their own answer, they can only accept answers by others, I'll repost your solution in case you'd like to Accept the answer.
- You determined you issue was the result of insufficient permissions and the use of wrong ADOMD (ActiveX Data Objects for Multidimensional Data) version.
- You were using version 13 and switched to version 16.
- You adjusted your Function app's rights to access the tabular model on your Analysis Services instance.