If you are testing your autoresponder integration optin form and you receive the following error (or similar - you may see a 404 error)
The Requested URL /process-optin-form/ was not found on this server
How to fix this problem
This issue is usually caused by you not having the correct Permalink structure inside WordPress.
You need to go to Settings > Permalinks and select the "Post Name" option and save this. This will ensure that OptimizePress can run the submissions script to submit the data from your opt-in form to your autoresponder or mailing list service.
LeadPages & 404 Plugins
If you are using any plugin which intercepts the 404 pages inside of OptimizePress, these can break the form submission process inside OptimizePress
We recommend either disabling these plugins if you have problems, or turn off their 404 page functionality to stop them interfering with the OptimizePress opt-in form submission process
We have seen this issue occur if you have entered URLs for either the thank you page or already subscribed page and have not included http:// or https:// at the start of your URL: