Local Viking seems to have been shut down by Google. Here is a Local Viking alternative for scheduling Google My Business posts that is in full compliance with the GMB API, and does NOT require you to apply for your own GMB API access.
OneUp: Local Viking alternative
OneUp is a Local Viking alternative for scheduling Google My Business posts and posting to multiple GMB locations at the same time.
When you sign up, you can connect your Google My Business listings from the Accounts page in OneUp.
Schedule a GMB post
You can post to one or multiple GMB locations at the same time with OneUp.
Go to “Schedule a post”, choose which GMB locations you want to post to, then add your caption and image.
You can even choose to have your Post’s image added to the Photos section of GMB.
Event posts are supported as well.
Next add your Call-To-Action button and a link.
You can also set your GMB posts to automatically repeat at whatever interval you choose.
Then either Post Now, or schedule it for the future.
Here is what that post looks like on the Google search results page.