  Let $G$ be a direct product of inner forms of general linear groups over
non-archimedean locally compact fields of residue characteristic $p$ and let
$K^1$ be the pro-$p$-radical of a maximal compact open subgroup of $G$. In this
paper we describe the (intertwining) Hecke algebra $\mathscr{H}(G,K^1)$, that
is the convolution $\mathbb{Z}$-algebra of functions from $G$ to $\mathbb{Z}$
that are bi-invariant for $K^1$ and whose supports are a finite union of
$K^1$-double cosets. We produce a presentation by generators and relations of
this algebra. Finally we prove that the level-$0$ subcategory of the category
of smooth representations of $G$ over a unitary commutative ring $R$ such that
$p\in R^{\times}$ is equivalent to the category of modules over
$\mathscr{H}(G,K^1)\otimes_\mathbb{Z} R$.
