Assuming for the sake of argument this were a real service checking for matches, the chances of a hash collision with SHA256 is effectively 0.[1] I entered the limit for BIGINT (9223372036854775807), and the approximation of the probability of a hash collision after generating 9223372036854775807 items in SHA256 is zero. The exact probability would probably take eons to calculate, but it's vanishingly close to zero.
nativeit|8 months ago
1. https://kevingal.com/apps/collision.html