Unable to edit personal records via Garmin Connect Web

I am trying to add a personal record which wasn't recorded by my Garmin using this page: https://connect.garmin.com/modern/personal-records.

I am able to enter a value in the "Record" field, and click the green arrow to confirm:

However, the "Send to Device" button is greyed out, and when I navigate away from the page, the form is reset without saving my record.