Zoho Creator Form Captcha Not Working on iPad

Zoho Creator Form Captcha Not Working on iPad

Hi

We have had several users complaining that the following embedded form Captcha does not work an iPad:

http://www.rentlondonflat.com/property-application

We have tested this and can confirm the Captcha does not seem to be accepted on an iPad.
But same form works on laptop or Samsung Pad.
So error seems specific to an iPad.

Please advise.

Thanks