Voronoï summation for GLn: collusion between level and modulus

We investigate the Vorono\"{\i} summation problem for ${\rm GL}_n$ in level aspect $n\geq 2$. Of particular interest are those primes at which and modulus jointly ramified, a common occurrence analytic number theory when using techniques such as Petersson trace formula. Building on previous legacies, our formula stands most general of its kind; we extend results Ichino-Templier. also give classical refinements study $p$-adic generalisations Bessel transform.