The "Something went wrong when executing the Add-on" error usually appears when the mobile add-on isn't correctly installed.
You should be able to fix this error by doing as follows:
- On your computer, click your photo in the top right corner while in Gmail
- Click Manage your Google Account.
- Select Security in the left navigation
- Click Manage 3rd Party Access.
- Select Mailtrack for Gmail Add-on > Remove Access.
- Install the Gmail Add-on as per the steps in this FAQ.