Hi umimeher,
Sorry for the late response. The "Shared Customer Contacts" option is simply a filter view for the contacts grid. This option will show all contacts that you have permission to view. The stock screen does not contain an "All Contacts" filter. My guess is that this is a custom filter view that was not setup correctly on your screen.
I believe the reason that you are receiving the error "please try again if the problem is persists sign out sign in and try again..", is that you did not link the contact to an Entity. You must supply an Entity when creating a contact for this to work correctly. If the Entity does not yet exist, you can create it by using the MethodAPIInsertV2 endpoint for the Entity table or one of its views (Customer, Vendor, Employee or OtherName).
I hope this helps.
--Audisho