The URL template.xsn is an unsupported relative URL error in SharePoint online modern form library

This SharePoint Online tutorial we will discuss how to solve The URL template.xsn is an unsupported relative URL error in SharePoint online modern form library.

If you are new to SharePoint modern experience check out the below tutorials:

• SharePoint Modern Experience – All You Need to Know!
• SharePoint Online Switch from classic experience to modern experience (List & Document Libraries)
• Impact on InfoPath in modern UI in SharePoint online office 365
• How to set modern home page in classic SharePoint site in SharePoint Online Office 365?

Recently we had migrated one InfoPath form from one environment to another environment in SharePoint online site. The form was published to a SharePoint online form library.

Now when going to the library settings and then click on “Advanced Settings” which is under General Settings. Then click on “Edit Template” which is under “Document Template” to open the form in InfoPath designer 2013 like below:

But instead of opening in the InfoPath 2013 designer, it gave the below error:
There has been an error while loading the form.
Click Try again to attempt to load the form again. If this error persists, contact the support team for the website.
Click Close to exit this message.

And in the details error message the error was like below:
The URL FormLibraryName/Forms/template.xsn is an unsupported relative URL. To fix this problem, use a site-relative URL starting with ‘~site’ or a site collection-relative URL starting with ‘~sitecollection’. You can also use an absolute URL. See the fig below:

The URL template.xsn is an unsupported relative URL

We figure out that the problem is happening if Modern experience has been enabled for the form library. So we changed to the classic mode of the library. And then we were able to open the form using InfoPath designer 2013.

You may like following SharePoint InfoPath tutorials:

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• Microsoft InfoPath Views Tutorial
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• Make attachment field mandatory in InfoPath Designer 2013 in SharePoint Online list
• SharePoint online InfoPath error The form cannot be submitted to the specified SharePoint document library
• InfoPath failed to publish because the default content type in the document library is not based on the Form content type SharePoint Online InfoPath Error
• This feature requires SharePoint 2010 or greater with InfoPath Forms Services enabled
• You do not have permissions to access a SharePoint list that contains data required for this form to function correctly

I hope this will help to resolve an error The URL template.xsn is an unsupported relative URL in SharePoint Online InfoPath 2013.