@DamienT Not sure if this a web 403 error code.  If it is, 403 error codes are usually related to access and permission authorization.  Would you be able to elaborate more on your workflow design and connections, so that the community can direct on potential problem area. 

@Sasan Thanks for dropping in Sasan. I spent a bit more time dabbling and found that the issue was with the Sharepoint lists and libraries connector. I reconfigured with an admin service account and was able to publish the workflows correctly. Seems that the account previously used for the connector didn’t have access to one of our sharepoint sites. All good now :)

@DamienT  glad it worked out.

Today, I’ve faced an issue with this error 403. The account used in the connector was site collection admin but I was getting the error 403 anyway. Checking the site collection admins, the account was member of 1 AD group. After adding the account name individually as site collection admin, the issue was fixed in Nintex Automation Cloud.