This is what you need to do.
When a member clicks on the button, add something to the database. You can do this with the wixData.save() api.
Then in the then after the save write this -
import wixData from 'wix-data';
import wixUsers from 'wix-users'
// ...
let toSave = {
"title": "Mr.",
"first_name": "John",
"last_name": "Doe"
};
wixData.save("myCollection", toSave)
.then( (results) => {
let items = results.items; //see item below
let count = items.length
if (count >= 60) {
}
} )
Then inside that .then((results)) you need to get the users plans and cancel the first plan they have. https://www.wix.com/velo/reference/wix-paid-plans/cancelorder