Error Message: "Please install All-In-One WP Migration plugin and submit the form again."
What causes this?
The All-In-One WP Migration plugin is either not installed or not activated in your WordPress dashboard.
How to fix It
Go to WordPress Dashboard → Plugins → Add New.
Search for "All-In-One WP Migration".
Click Install and then Activate the plugin.
Once installed and activated, try submitting the migration request again.