The lack of the button is due to the following reasons:
If you use the app
1Control SOLO
Your device belongs to the first generation of products and the advanced management of shares is present only in the PRO or FILO models.
Otherwise if you use the app
1Control
Sharing is only possible if you are an administrator of the device.
Administrators are users who have logged into the SOLO using the PIN code.
Administrators are users who have logged into the SOLO using the PIN code.