Hi @Fareed J , thanks for your question. Please review these two documents:
Did you only change the permissions in Azure AD? You most likely also need to configure the guest permissions within Power Apps. In Azure AD, what permissions did you assign? You must assign both read and write permissions.
If these suggestions don't work, please open a thread on the Power Apps forum. I beleive this is more related to Power Apps than AAD.
Please let me know if you have any questions!
If this answer helped you please mark it as "Verified" so other users can reference it.