I use Convert Plus to subscribe readers to our newsletters. Some people, when trying to subscribe, get a message "THERE WAS AN ISSUE WITH YOUR REQUEST. The administrator has been notified already." This happens on my www.woodtech.events website with all my subscription forms (side bar, footer and homepage button pop-up).
As the 'admin', I didn't get a message. Their email was added to the Convert Plus contacts list, but not added to my linked MailChimp list and no email was sent to confirm their subscription.
It does not happen everytime, but I can replicate the issue. I entered my gmail address and used the + symbol to do a test subscription (ie firstname.lastname@example.org). The error message appears most times.
My theme and plugins are all updated and I have purged the cache several times while trying to solve this. The Connects - Mailchimp Addon is on version 2.1.1. There is a version 2.2.1 available, however the X Pro theme cannot update to this.
I did a quick web search and did find the same issue (but no solution that worked) on:
I use Convert Plus on a number of different websites, so important to find a fix.
In a maybe related issue, I found out that all the Convert Plus subscription forms disappeared for the public on at least two of my websites. I needed to re-add the forms to the website. This has already been done.