Is there a way to match the userID (phone #) of the incoming user by using the Webhook/HTTP to look up and see if there is a match?
Webhooks typically are used to connect two different applications.
In what you would like to achieve, you need to match phone number to a certain database, we do have direct /easy integrations with different database or communication apps ( ex. google sheets) you can use without creating a webhook.
Please see list : https://support.flowxo.com/category/3-integrations