IPv4 and IPv6: what changes when you use a proxy
Our addresses are IPv4; the difference shows up at the destination.
IPv4 is the four-number address that still moves almost the whole internet. IPv6 is the longer address, created because the four numbers ran out. A site may have both, only one, or neither.
Where this touches your work
The addresses in this service are IPv4. When the destination site is IPv6, the connection can leave without going through the proxy, because the system tries the IPv6 path first and finds no address there. That is how a good line becomes "it does not work on this site".
To force the traffic through the proxy, the program has to use the protocol on the right port. HTTP on 20001 and SOCKS5 on 20481 are IPv4: with the right address, the destination sees IPv4.
How to check
Run the proxy test on your address: the sheet shows the exit IP the destination received. If it differs from the address of the line, the connection did not go through the proxy.
The block list check is IPv4: fourteen public lists are queried in the four-number format. An IPv6 address answers that the check is IPv4 only, without inventing a result.
When you need IPv6
If the project requires IPv6 at the destination, the way is the ticket: we say what exists that day before you buy. Promising a range we do not deliver helps no one.