If you enable any only payment method like as Stripe, PayPal or Paytm, the payment options will show on the invoice preview page on the client portal.

Online payment methods are only visible to clients, while offline payment methods are only visible in the admin portal.

Pay without login

You can also send the invoice link to clients via email. In this case, the client can view and pay the invoice without logging into the client portal. The online payment options will be available directly on that public invoice page.

To enable this feature:

1. Go to Settings > Sales & Prospects > General
2. Enable the option: Client can pay the invoice without login
3. Then, update the Send invoice email template by adding the variable: {PUBLIC_PAY_INVOICE_URL}

This will include a direct payment link in the email, making it easier for clients to pay their invoices quickly without login.

Custom payment methods

You can create custom payment methods from Settings>App settings>Sales & Prospects>Payment methods. 

If you add a payment method from this section, it will be treated as an offline payment method and will only be visible in the admin panel.

If you're looking to offer an online payment method that clients can select and use directly, you'll need to create a plugin for it.