Originally Posted by
kevinsac
I arrived in FRA very early morning
If you arrived in LH C or F, you had access to the Business lounge or F lounges as a part of LH's arrival services. Just show your BP stub.
If you arrived on UA, you could have used UA's arrival services in FRA.
Also, buying a ticket at a German counter involves a nonrefundable TSC, and since you bought 2 tickets, you probably paid around US$100 in order to get into the SEN lounge.
I hope it was worth it.