How is the deposit System Made?

Hey y'all, Hope you guys are doing well

I have seen many websites which use crypto payments,

Some Deposit Systems Works Like this:

1. They don't ask for the deposit amount

2. They show you a permanent deposit address

3. when the user sends any amount to the deposit address

4. When the amount is detected and is added to the account or something is processed ( webhooks or IPN )

5. I want to know how it is made or which gateway they

I may be sounding silly with this, as you can say there are many payment gateways

But after some research, I found the following

1. Several Gateways are required to input the amount, not gateway works without the amount ( as per my observations )

2. Some work with APIs but they also require to input the amount ( Deposit amount ) Which isn't how it works on many websites

3. Some examples: coinpayments ( it provides a deposit gateway without amount but works, so I can confirm in several places that it is not used )

4. No Other gateway I found works in the way I stated.

Some Examples :

We Can Send any Amount Above the minimum

Here Too

Here too

Basically, I mean to Say, How they are made,

they deploy a node or some sort of gateway to make such a deposit system where we receive callbacks after every deposit , I am unable to find one or don't know how to work with the nodes

I wanted to know if you know any thing about it , how to deploy such nodes and work with deposits and getting callbacks with every deposit made on node

Thanks,

I hope you guys understand what I meant to say