Can you send me a screenshot of this issue?
You can send screenshot to support@nextscripts.com or just paste it to http://snag.gy/ and give me the link to it.
Please just follow our very detailed and illustrated with many screenshots step-by-step instructions:
https://www.nextscripts.com/instructions/medium-auto-poster-setup-installation/
This error is a common mistake and it is well explained in those instructions. Please see the “Troubleshooting note” in #3.2
thanks the casing was indeed wrong. It’s not clear from the help that I have to copy and paste the wordpress plugin page URL
