Hi, some gridcodes at the SUN2000 settings do not allow frequency shifting I think. Here is the screendumps of the location where to adjust settings.
Be aware that page is an example, so displayed values differ from my actual settings, als the 100% i set to 0%, My settings are 50.2, 51.48 and 51.5hz. Also I entered the inverter with SUN2000 app , not the fusion solar app. Never tried with fusion solar app for this. I do use fusion solar app for monitoring pv.
All of this is already explained in this community on Multiplus II and Huawei AC-Coupling