My website is built entirely with custom HTML / CSS, and I need a lightweight payment module added. Visitors must be able to choose between PayPal, Revolut or a direct bank transfer, each presented as its own button. After a successful payment the system should: • generate a clear receipt (PDF or HTML) • email that receipt simultaneously to the client’s Gmail address and to ours • log every enquiry plus full payment and transport details into a secure MySQL table that I can review or export to CSV later I already hold active PayPal and Revolut accounts alongside a standard merchant bank account, so credentials will be supplied once your structure is in place. Please keep the code framework-free—plain PHP, JavaScript and the relevant PayPal and Revolut APIs—so I can drop it straight into existing pages. Robust error handling and friendly success / failure messages are essential. When replying, show examples of similar multi-gateway checkouts you have built and outline how you would handle the database schema and email generation.