Experiments with externally-applied magnetic perturbations (MPs) have been carried out in MAST-U to study the effect on the fast-ion distribution. Scans performed of the current applied in the coils, the toroidal phase offset between the currents in the upper and lower coil sets, and of the absolute phase of the perturbation for two different sources of fast ions are presented and discussed for an n = 2 perturbation. The results indicate a modulation of the FILD signal with the applied perturbation, which is determined by the three scanned parameters, and also by the velocity-space of the fast-ion losses, suggesting a resonant interaction between the MP and the fast-ion orbits. To study this interaction, MARS-F has been used to compute the perturbed fields and the resulting magnetic field has been used as input in the modelling of first-orbit losses performed with ASCOT. The analysis of the fast-ion transport indicates that the resonances that overlap at the edge of the plasma may be responsible for the losses, in agreement with previous results from ASDEX Upgrade. Furthermore, simulations predict a modulation of the losses reaching FILD with the applied configuration, but with minima/maxima at phases opposite to those observed experimentally. This suggests that all non-axisymmetric field components, such as intrinsic error fields, need to be included in the MARS-F modelling, as well as all toroidal components of the perturbation.