How to grant access to IP range in Postgres?
The /128 in the address is the NUMBER OF BITS to match...  not a range.

So you would want 10.8.101.0/24 (match the first 24 bits).

As an additional example, if you wanted to restrict it to 10.8.101.128 to 10.8.101.255 then you'd do 10.8.101.128/25

Please see the address subsection in the documentation