Problem description: model size too large
Umbra currently limits the size of the models that can be uploaded to make sure computations succeed in a timely manner.
Umbra only uploads what's visible in the 3D View. Therefore limiting what's visible in the 3D View, for example using a Section Box in Revit, will allow for the computation to go through.
The limit on data size currently isn't defined as an area, but rather total volume of content. Therefore it is difficult to estimate what will go through; start off by selecting on the most essential part of your model and uploading that to a View Slot, and then expanding the crop to other view slots.