the basic idea would be something like this
let table = base.getTable("Table Name")
let record = await input.recordAsync("Select a record", table)
if(record && record.getCellValue("Checkbox Field") === true) {
let url = "insert webhook url here";
await fetch(url + "?recordID=" + record.id);
output.markdown(`## Record sent to Zapier`)
} else {
console.error("record not selected or value is not true")
}