There are a few ways to fix the "oops something went wrong" error; usually when you encounter this issue it isn't due to a problem within the plugin, but with your settings. Here are a couple of ways you can check if something might be missing or incorrect.
Check the MailChimp for WordPress log
Log in to your WordPress Admin and go to MailChimp for WP > Other. Check to see if there is any error explaining why the form did not submit. For example the email address could be blocked by MailChimp.com or be marked as fake email.
Check the MailChimp.com API log
Log in to your MailChimp.com account, click on your account name on the right top and choose Account.
Click on Extra > API keys. Scroll down to see the latest calls to the API and their result.
Check your MailChimp settings
Check is if every field you're using in your form is also present in your MailChimp's List fields and *|MERGE|* tags page, and that you're using the correct settings. You can find this page in MailChimp Dashboard > Lists > Your list > Settings.
Check the following:
- Are you using the correct tags in your form? You should be using the tags mentioned under #5 (see below)
- Do you have a field set to required in MailChimp, but not in your form? (Check #3)
- Are you using the correct field type in your form (see #2)? If, for example, you have a
type="text"in use for your website input field, MailChimp will return an error.
The plugin checks for these things and will actively notify you if it finds anything wrong, but it's a good idea to check everything if you run into trouble.
Fix the error in custom forms
When you are using a custom form, or are integrating with Contact Form 7, there are a few other things to check for. Make sure you have checked everything listed above first (you will not receive error messages when you're using another plugin!).
If the issue still persists, make sure you have prefixed every field that you would like to send to your list with