Before you get too far to writing code, I will recommend you order a Prefix by Microsoft. Click here for more informations 
You can order it by writing an email to

I had written a lot of code for my App/extension before I became aware of that a Prefix was a requirement to publish an Extension to Appsource.

It was a relatively big job to go through all the code to correct it 🙂

Range ID

If you want to publish an extension to Appsource you must also order a object range at Microsoft, Range ID must be between 70,000,000-74,999,999.
I am in the process myself of ordering a Range and will share my experiences later on here.

Written by Michael Fröhlich