No account needed: every booking and every group has its own private link.
Open the link from your confirmation email or WhatsApp message. It starts with the property's address and /stay/. From there you can pay the advance, cancel within the policy, and review after your stay.
Organisers keep the link that opens at /g/…; members use the personal link they got when joining. Lost it? Ask your organiser to resend the invite link: joining again with the same phone or email gives you your own link back.