After clicking buy button , Express Wifi will send the below
{
“amount”: 1.00
“currency”: ZWL
“hmac”: [ to be calculated backend ]
“timestamp”: [ to be created by backend ],
“payment_id: 11931233524,
“callback_url”: “https://expresswifi.fb.com”,
“phone_number”: “+263772000000”,
“source”: “customer”
}