the only problem
That’s not the only problem.
It wasn't the only problem.
El único problema era que para todo el mundo, él ni siquiera existía.
The only problem was that, to everyone else, he didn't even exist.
— La leyenda del pianista en el océano (1998)
Este no era el único problema.
This was not the only problem.
That wasn't the only problem.
El único problema es conseguir una llave.
The only problem is getting a key.
— Uno de los nuestros (1990)