On Apps Script Menu Bar, go to Resources > Cloud Platform project...
On Google Cloud Platform, go to the left navigation menu Select APIs & Services > Library
In the search bar that appears, type in "GSuite Marketplace SDK" Hit Search, once it appears click it.
Click on "ENABLE"
Once you click Enable in step 4. the screen below should appear. Select "CONFIGURATION"
Fill the document as you deem fit, but the most important part is shown below.
Scroll Down to Editor Add-on extensions, then select the Google App you're building your add-on for. It's the same process for Docs, Forms Sheets or Slides Add-ons
How to Get Script Project Key. Go back to your Apps Script Page.
Go to File > Project properties. Select the 'Info' tab. Then copy the value of Project key (Deprecated) and paste into the "Script Project Key" field
How to Get Script Version. Still on your Apps Script Page.
Go to File > Manage versions....
Then copy the value of Version and paste into the "Script Version" field
Click Save Changes and voila you're done. Do not forget to add the privacy policy URL and other required info, else the changes will not be saved
Gosh... not sure why this was so hard. It'd be more user-friendly to run the various API checks before the user selects to publish their add-on and/or provide a link to the correct documentation! Then fix that super cryptic error message.
Anyway, for others who are stuck in this boat (like me who published their first add-on so long ago they'd completely forgotten about this step) here are the most up to date instructions. (Thanks Tanya Gupta for putting me on the right track).
Step 1: Enable the GSuite Marketplace SDK
Follow these steps:
From the Script Editor, open the Resources menu item then select Cloud Platform Project
Click the button View API Console (you can also click the link with your project ID)
Click the hamburger (navigation) icon on the top left and select "APIs & Services" then "Library"
Search for "GSuite Marketplace SDK". It's important you install the SDK (software development kit) not the API.
Click the ENABLE button
You should now be able to see an option for Configuration in the menu on the left.
Step 2: Configure the GSuite Marketplace SDK
For configuration you will need to:
select at least one language and enter an application description (for your add-on). The name should be pre-filled and match your script name.
upload some icons of various sizes
add a Terms of Service URL (if you don't have a website then just create a public Google Doc)
enable at least one Add-on extension
When you enable the Add-on extension, you will need to provide the following information:
Add-on Script Project Key can be found from the Script Editor. Go to File > Project Properties and copy the value for Project key (Deprecated)
Add-on Script Version is the version of your script. You can find the version in the Script Editor. Go to File > Manage Versions and select the latest version of your script.
Note: your add-on script version will be updated automatically when you publish new releases of your add-on.
If you are publishing on Google Apps Marketplace, you need to not only enable the API, you also need to configure it by entering the needed settings.
1) First click on the enabled API as per image below:
2) Then click on configuration.
3) Then fill out the values as per below:
4) Particularly important are (not shown here):
a) including correct oauth scopes (File->Project Prop->Scope from your script file)
b) Docs Add On Project Key (File->Project Properties->Info->Project key)
c) Docs Add On Script Version (from the developer console)
Now if you go back and publish you should no longer have the error
I've created these instructions https://docs.google.com/document/d/1gG0_EClZC4ztKHDT2yn8v9NmUh_-sqYFe9vGg6Snxgg/edit?usp=sharing based on answers given here and other weeks of trial and error - I hope they someone headache that I had to go through.
Just to build on Dagmar's Answer
Solve this issue in 8 steps with Pictures:
Fill the document as you deem fit, but the most important part is shown below.
Scroll Down to Editor Add-on extensions, then select the Google App you're building your add-on for. It's the same process for Docs, Forms Sheets or Slides Add-ons
Go to File > Project properties. Select the 'Info' tab. Then copy the value of Project key (Deprecated) and paste into the "Script Project Key" field
Go to File > Manage versions....
Then copy the value of Version and paste into the "Script Version" field
Gosh... not sure why this was so hard. It'd be more user-friendly to run the various API checks before the user selects to publish their add-on and/or provide a link to the correct documentation! Then fix that super cryptic error message.
Anyway, for others who are stuck in this boat (like me who published their first add-on so long ago they'd completely forgotten about this step) here are the most up to date instructions. (Thanks Tanya Gupta for putting me on the right track).
Step 1: Enable the GSuite Marketplace SDK
Follow these steps:
Step 2: Configure the GSuite Marketplace SDK
For configuration you will need to:
When you enable the Add-on extension, you will need to provide the following information:
Note: your add-on script version will be updated automatically when you publish new releases of your add-on.
Google documentation: