The authors consider a nonlinear Robin boundary value problem \[ - \Delta_p u(z) + \xi(z) |u(z)|^{p-2} u(z) = f(z,u(z))\quad\text{in}\quad\Omega,\quad \frac{\partial u}{\partial n_p} + \beta(z) |u|^{p-2} u = 0\quad\text{on}\quad \partial\Omega, \tag{\(*\)} \] where \(\Omega\) is a bounded domain in \(\mathbb{R}^N\) with a \(C^2\)-smooth boundary \(\partial\Omega\), \(\Delta_p\) is the \(p\)-Laplace differential operator and \(\frac{\partial u}{\partial n_p}\) is the generalized normal derivative defined by the extension of the map \[ u\mapsto \frac{\partial u}{\partial n_p} = |D u|^{p-2} (D u, n)_{\mathbb{R}^N}\quad\text{for all}\quad u\in C^1(\overline{\Omega}), \] with \(n(\cdot)\) being the outward unit normal on \(\partial\Omega\). Assuming that \(\xi(z)\) is a sign-changing \(L^\infty(\Omega)\)-function (indefinite potential), \(f(z,u)\) is a Carathéodory function and \(\beta(z)\) is a non-negative Hölder continuous function, they study the existence and multiplicity of nontrivial smooth solutions to problem (\(*\)) in the resonant case. The latter means that \(f(z,u) = \hat{\lambda} |u|^{p-2} u + g(z,u)\), where \(g(z,u)\to 0\) as \(u\to\pm\infty\), and \(\hat{\lambda}\) is a variational eigenvalue (i.e., \(\hat{\lambda}\) is such that the problem (\(*\)) with \(f(z,u) = \hat{\lambda} |u|^{p-2} u\) has a nontrivial solution). The analysis of problem (\(*\)) relies on variational tools from critical point theory as well as on Morse theory.