Why do I have low recording volume when using external mic to record video on iPhone 6 plus?

[iMore Question]

Hi - I am using an external Rode lav mic to record the audio for interviews on the iPhone6 plus. The recording volume is very low. I replaced the battery on the mic and also tested it on my old iPhone 5. It works much better on the 5. So that makes me think that its not the mic but its the phone. Any ideas?

 

[kch50428]

This might be one for an Apple Genius Bar...

 

[simone2017]

Same problem here with an Iphone 6s plus. How did you solve it?
Thanks