In the Logunov-Tavkhelidze quasipotential approach, convergence of the iteration procedure for taking the dynamic retardation effect in the electromagnetic form factor into account is investigated for a bound system of two scalar particles interacting via a separable Bethe-Salpeter kernel. The status of the relativistic impulse approximation within the framework of this approach is discussed. In the static approximation, the electromagnetic vertex operator obeying the current conservation and normalization conditions is constructed, taking the interaction current into account. A comparative analysis of the form factor in different approximations is carried out.