Unfortunately the Trust this Add-In button leads to a crash of Excel, so it does not work at the moment (Excel Version 1903 Click-to-run):
To activate the data1.io Web Add-In please use the Get Add-Ins command in the Insert Ribbon (please note that this command is available only in the newer Excel versions and was called Store in the earlier versions):
Now search for data1 and click the Add button to install the data1.io Add-In to your Excel Client (more precisely the Add-In is added to your MS Office user account and the Add-In will be activated on all your devices with MS Office as well as in Excel Online):
After adding you`ll find the data1.io Add-In in the My Add-Ins section (of the Office Add-Ins dialog) and the button Show Taskpane will be displayed in the ribbon Home:
Now press this new button and the data1.io Taskpane will be started:
From now on the Add-In can be started with this button if it not is not anyway started automatically when the template file is opened.