Only do this on a network you already trust (home, cellular, or one you've just confirmed on the Verify Connection tab). The code pinned during this install is what protects you on networks you use later — if this first install happens on a hostile network, the pinned code is already compromised.
This must match the passphrase configured on the server (ask the operator, or check SITR_APP_CRYPTO_PASSPHRASE if this is your own deployment).