Zoho calendar not syncing on iPhone

Zoho calendar not syncing on iPhone

I have zoho calendar & email on my iPhone and iPad. The calendar is not syncing on my iPhone, but it works fine on my iPad. No issues with mail on either device. I have tried deleting from both and only installing on iPhone but it still doesn't work. iPad running 7.0.2 (have not upgraded yet) iPhone running 7.0.3 I am thinking this an issue with the newest version of iOS but need it to work. I have set it up with Microsoft exchange server settings using msync.zoho.com Please advise