Range Query with conditions
Since there are no updates there is a rather simple solution. Store a map of key -> array of pairs, such that for every element in your original vector (value, key) at position pos, you store in the vector associated with given key in the map the pair (position, value). Keep every vector sorted by position.

For example in the input array: $$[(3, 1), (2, 3), (2, 5), (1, 6), (3, 3)]$$ you would build the map:

{
    1 : {(4, 6)} // (value 6 at position 4)
    2 : {(2, 3), (3, 5)}
    3 : {(1, 1), (5, 3)}
}


Notice that with this data structure you can solve queries in vector by finding the sum in suffix. First find the corresponding vector in $O(log N)$ (possible in $O(1)$ if used unordered_map instead of map) and use lower_bound (also in $O(log N)$) to determine the target suffix. You should keep cumulative sums of the vector to calculate the sum on a suffix in $O(1)$.



To handle updates of the form add an element of the form (key, value) to the end of the original array you should only extend the vector corresponding with key in the map. You know the new position in the original array, which is greater than all previous position since it is at the end, so add the pair (new_size, value) to the end of the array associated with given key.

Notice that we must keep cumulative sum up to date, but cumulative sum up to the first $n$ values is equal to the cumulative sum up to the first $n-1$ values plus the last value. The new cumulative sum can be computed in $O(1)$.

Notice that in practice we don't need to have on each vector in the map a pair of (position, value), but instead (position, cumulative_sum).