woocommerce-paypal-payments/modules.local/ppcp-onboarding/assets/js/onboarding.js

function onboardingCallback(authCode, sharedId) {
    fetch(PayPalCommerceGatewayOnboarding.endpoint, {
        method: 'POST',
        headers: {
            'content-type': 'application/json'
        },
        body: JSON.stringify({
            authCode: authCode,
            sharedId: sharedId,
            nonce: PayPalCommerceGatewayOnboarding.nonce
        })
    });
}