no implicit conversion of nil into String

I am trying to cancel my account, as we use PollUnit once per year for a charity event, but am unable to, as I get the following error: no implicit conversion of nil into String. I am sending through an email now, but, as it's a charity event, we're keen to not have any unnecessary billing as that decreases the total to donate! Thank you!

Hi,
We are sorry! There was a glitch in our system.
It is fixed now and I cancelled the subscription for you.
Kind regards
Philipp