When you send a call sheet, every person on it receives their own confirmation link. It works without a Tubes account.
What the crew sees
The email asks "Can you make it?" with two buttons: Yes, I'll be there and I can't make it. The link opens a small page that records the answer, and the same link can be used later to change it. Links work for 30 days; after that the planner can send a new one.
What the planner sees
In the activity panel, each person shows Pending or Confirmed. When everyone has answered, the day shows "confirmed". A decline is noted so you can find a replacement.
Send a link by hand
Next to a person in the day you can copy their confirmation link, valid 30 days and no login needed, to send it by WhatsApp or another channel.
Tip: Confirmations are per person per day. Duplicating a day does not copy the confirmations; the new day starts as pending.