Here are the suggestions
- Check that you have download the package for the right version of SharePoint. You need Office 365 version: "SharePoint Online (Office 365)"
- Do not double-click the sppkg. This is not an installation program and that's not going to be installed by doing so. Instead, follow the instructions on their website
Org Chart is a SharePoint Framework add-in that allows you to
visualize organization structure on both classic and modern SharePoint
pages. Unfortunately, SharePoint Store doesn’t support the
installation of SharePoint Framework add-ins. That is why you need to
install add-in manually.
You have to be a SharePoint administrator to complete the
installation. If you don’t see some menus from the instruction below,
most likely you are not a SharePoint administrator. Please contact
your administrator to assist with the installation.
Open Office 365 admin center:

- Navigate to SharePoint Admin Center:

- Go to ‘Apps’ classic feature:


- Open App Catalog
- If you don’t have ‘App Catalog’ yet, you will be able to create a new one:

Just fill in ‘Title’, ‘Web Site Address’, ‘Administrator’ and ‘Storage Quota’ and click ‘OK’. For example:
- Title – App Catalog Site
- Web Site address – AppCatalog
- Administrator – Fill in your account name
- Storage Quota – 10 GB

Navigate to ‘Apps for SharePoint’ and upload Add-in package that you downloaded at the beginning of this instruction (you need to upload to the App Catalog the whole .sppkg file without unpacking it):

Upload App To Catalog
You need to select “Make this solution available to all sites in the organization” in the dialog. Once you did this you can add a web part to a page.

If you don’t want to make this app availalbe on all sites, you will need to add app to each site manually.
Adding web part to a page
Navigate to the page where you want to add an org chart.
Note: If you use “Classic” SharePoint pages follow this instruction to add web part to a page.
Pick ‘Plumsail Org Chart’ web part from the menu to add it to your page:
Add Modern Org Chart WebPart