I tried creating a plan for the existing group using Microsoft Graph Explorer, it was created successfully. Again I tried to create an another plan for the same group it threw me an error saying "MaximumPlannerPlans".
But I used the same code which I tried in the Microsoft Graph Explorer, in my SPFx webpart using GraphHttpClient for creating multiple plans, it is allowing me to create multiple plans for the same MS Group. Is it a bug or an expected behavior? If it is an expected behavior then why it is not allowing me to create multiple plans in the Microsoft Graph Explorer?
I am using same user login for the both SPFx webpart and Microsoft Graph Explorer which has an owner access.