The documentation for MMW is quite clear in that 'wfsIdColumnName' is the "Name of the column which contains WFS FeatureID values. It is required for the synchronization with WFS-T." When configuring a Read-Write Vector Layer for cache and synchronization we follow the documentation an see an example there indicating a column of 'rid' for this value. We do not believe this column exists in our WFS. How do we determine what our WFS should use for 'wfsIdColumnName'?
it is correct that the documented example for configuring a Read-Write Vector Layer Working on Vector Cache uses (rid) is an example for wfsIdColumnName. This is for illustration purposes only and may not match to your specific WFS case. To determine the attribute column for your WFS there are a couple of ways to go about it.
Once the correct wfsIdColumnName is determined, plug it into your MMW configuration and save the file to ensure the cache GPKG can communicate and synchronize with the WFS as intended.