Sync between Potentials in ZOHO CRM and ZOHO Campaigns (to send a survey)

I want to send an e-mail inviting customers to take a survey.

The e-mail should be sent to everyone from a specific survey who has purchased from us recently.

The sync is set to retrieve all contacts for potentials in a specific territory, where the potential status is Won. Initially I had entered an 'modified after...date' criteria too, but removed this to get to basics.

No data is transferred.

I've checked that all the potentials have a contact.

I've checked that the territory is listed correctly.

I've even collected them all in a view using these criteria to double check.
Still no data is transferred.

I can't figure out what I'm missing.
Can anyone help?

Thanks,

Karen