I would assume, starting your development journey in Odoo with a payment integration is probably not the best idea since you definitely want to make sure your payment integration is secure and fail-safe.

References, however, are available in two forms:

Documentation:

There is a section in the documentation, describing certain functions within the payment process

• https://www.odoo.com/documentation/18.0/applications/sales/point_of_sale/payment_methods.html
• https://www.odoo.com/documentation/18.0/developer/reference/standard_modules/payment.html
  
  

Existing integrations:

Also, there is a list of modules that implement payment methods in GitHub (https://github.com/odoo/odoo/tree/18.0/addons) that can be used as a cross-reference of how to integrate a new provider:

• payment_adyen
• payment_aps
• payment_asiapay
• payment_authorize
• payment_buckaroo
• payment_custom
• payment_demo
• payment_flutterwave
• payment_mercado_pago
• payment_mollie
• payment_nuvei
• payment_paypal
• payment_razorpay
• payment_razorpay_oauth
• payment_stripe
• payment_worldline
• payment_xendit