to be there just to make up the number 滥竽充数

“滥竽充数”，汉语成语，意思是不会吹竽的人混在会吹竽的队伍里充数（pretend to play the Yu [a wind instrument] in order to make up the number for an orchestra）。比喻无本领的冒充有本领，次货冒充好货（to be there just to make up the number [used of incompetent people or inferior goods]）。

例句：

我不会唱歌， 我在这儿只是滥竽充数。

I am not good at singing. I'm here just to make up the number.

宁可虚位以待，也不要让不称职的人滥竽充数。

We'd rather leave the place vacant than have someone incompetent fill the position.