When building an e-commerce website in PHP, it is important to integrate a secure and reliable payment method to handle online transactions. Here are some popular payment methods that you can integrate into your PHP e-commerce site:

1. PayPal:
PayPal is one of the most widely used payment methods for e-commerce websites. It allows customers to make secure payments using credit cards, debit cards, or their PayPal account. To integrate PayPal into your PHP website, you can use the PayPal PHP SDK or directly integrate the PayPal API.

2. Stripe:
Stripe is another popular payment method that provides a simple and secure way to accept payments online. Stripe supports credit card payments and also provides additional options like accepting Apple Pay and Google Pay. You can integrate Stripe into your PHP website using the Stripe PHP library.

3. Braintree:
Braintree is a full-stack payment platform that supports credit card payments, PayPal, Apple Pay, and Google Pay. It offers easy integration and provides robust security features for handling online transactions. The Braintree PHP SDK can be used to integrate Braintree into your PHP website.

4. Authorize.Net:
Authorize.Net is a payment gateway that allows merchants to accept credit card and e-check payments online. It provides the necessary tools to securely handle payment transactions. Authorize.Net provides AIM (Advanced Integration Method) which you can use to integrate it into your PHP website.

5. 2Checkout:
2Checkout is a global payment platform that supports multiple payment methods, including credit cards, PayPal, and local payment options. It offers a simple integration process and provides robust security features. You can integrate 2Checkout into your PHP website using the 2Checkout PHP library.

6. PayU:
PayU is a payment gateway that supports online payments in various countries. It provides a range of payment methods, including credit cards, debit cards, and local payment options. PayU offers easy integration options for PHP websites.

These are just a few examples of payment methods that you can integrate into your PHP e-commerce website. Each payment method has its own set of features, fees, and integration options, so you should choose the one that suits your specific requirements and target audience. It is important to carefully review the documentation and guidelines provided by the chosen payment method provider to ensure a smooth integration process.