There isn't one!
Pet insurance is a reimbursement plan so you can visit any licensed vet in the US! There is no network.
The next time you visit your vet you'll pay for your visit with the Nibbles card and have them email you a copy of your invoice, receipt, and veterinary notes. Then, you'll upload your documents and submit a claim on the Nibbles dashboard and you will be reimbursed for any items that are eligible for coverage.