JCurve mobile app is dependent on your Shopify setting.
To allow your customer to login or signup, you need to check your Shopify setting.
Shopify Admin > Settings > Checkout
2. In Customer accounts section, please check your setting. You need to check "Account are optional" or "Accounts are required"
3. Let's sync with mobile app! Final step.
Go to JCurve > SETTINGS > change your setting based on "Step 2"