How does client sync work between Nightingale and Xero?

There exists three syncing options for Xero which can be seen below

Do not create multiple contacts for clients that already exist in Xero

This option refers to the change that was made that allowed multiple contacts to be synced for a client which meant a client could have a plan and self manager or plan manager and invoice payer in Xero. Selecting this option stops the code from creating multiple contacts for clients that already exist in Xero. For example, you have a client called Penelope Smith, if you create her Contact card in Xero before doing the sync and have the first option selected, the sync will match the names between the systems, save the Xero Id against Penelope in Nightingale and move onto the next client. This option allows users to sync only clients to Xero and no contacts from Nightingale.

Sync Clients And Invoice Payer Contacts

This option enables the multiple contact sync so it will transfer over all contact payers that are on the client in Nightingale to Xero and will do so in the format [Contacts Name] - ([Clients Name]).

Sync Clients and Consolidated Invoice Payer Contacts

This option is similar to the above but the name of the contact in Xero will be just the contacts name and all clients that have that contact on their dashboard will have their invoices sent to that one contact in Xero.