Telethon: add contact by telegram ID

I can get a users unique telegram ID, for example by using GetContactsRequest or by get_entity. In some cases, I don't know a users unique telegram username or his phone number, but only this ID. How can I use this ID to add a user to my contacts on a different account, that has never communicated with the associated user before? When I try get_entity or AddContactsRequest with the previously obtained ID on a different account, I always get an error that this entity cannot be found.