REGEX-Escape for: /checkout.html?affiliate=F72&esid=2340842&fun=page&pagename=eventseries

Your Input:
Result, the escaped string:
\/checkout\.html\?affiliate\=F72&esid\=2340842&fun\=page&pagename\=eventseries

What must the escaping look like for:
/checkout.html?affiliate=F72&esid=2340842&fun=page&pagename=eventseries

The excaped text for use in a regex is:
\/checkout\.html\?affiliate\=F72&esid\=2340842&fun\=page&pagename\=eventseries