Try Gutenberg callout redirects to invalid page on multisite after activation

[earnjam]

On a multisite network, if you click on the "Activate Gutenberg" button on the Try Gutenberg callout, it uses self_admin_url( 'plugins.php?action=activate&plugin=gutenberg/gutenberg.php&from=try-gutenberg' ) as the URL to activate the plugin.

This network activates Gutenberg, which is probably fine, but it should maybe be more obvious that's what is happening.

However, after activation, we do a redirect using wp_redirect( self_admin_url( "admin.php?page=gutenberg" ) ). Since we just activated in the network context, this results in the URL being: /wp-admin/network/admin.php?page=gutenberg, which does not exist. The user sees a "Sorry, you are not allowed to access this page." error message.

We should use admin_url() here so it redirects to the demo page on the primary site, rather than trying to be in the network admin.

[earnjam]

Use admin_url() instead of self_admin_url() on the redirect

[pento]

Closing, as Try Gutenberg will be removed from the 4.9 branch.