A/B testing: How to calculate p-value on post test segments?
I recently wrote about this in a blog post.
Given this is a rate evaluation metric, you will want to use the z-test. The basic steps are (more details in the blog post)

calculate the pooled standard error of your pairwise comparison
calculate z-statistic by normalizing the delta or lift by the standard error
look up the cdf value of the normalized delta
p-value = 1-cdf(z)
given that this is also an A/B/n test, you should also want to apply multiple testing correction using the bonferroni procedure or the benjamini hochberg procedure, when evaluating significance