1. via generic session links
Call PUT (or POST to edit an existing) session, then use the returned session id to call a GET session. This will return session_link. This link is generic and carries no authentication data, so it will always prompt users to login (for registered users) or provide a screen name. It may also ask for the session password if one was defined.
2. via personalised session links
Call PUT (or POST to edit an existing) session and make sure to populate the invited_participants array.
Now there are 2 different approaches you can take:
i. Have OnSync send out personalised session links
In the invited_participants array, st send_email_invitation to true and the OnSync API will send out email invitations on your behalf. These email invitations are identical to those sent out through the Account Center and contain a personalised session link (unique to each invitee) which will load the session directly, without further authentication prompts.
ii. Have the personalised session links returned to you, so you can process them yourself
In the invited_participants array, set send_email_invitation to false and OnSync will not send out any email invitations. Then, call GET invitees with the session id returned in PUT/POST session to get a list of invitees, along with a personal_session_link for each. You can process this data as you want, and send out your own invitation emails, or store these links in your DB for later processing.
All the API methods referred to above are covered in the OnSync API documentation.