Answer
dbones resolves the "ContentPath and iisApp incompatible" error by switching the -dest option to use the contentPath provider, thereby making -source and -dest to have the same provider.
You can alternatively resolve the error by switching the -dest option to use the iisApp option. This works for example:
msdeploy -verb:sync -source:iisapp="C:\fooapp" -dest:iisapp="MyWebsite/fooapp",computerName=localhost
One advantage / difference of this method is that the first time you deploy fooapp, it will create MyWebsite / fooapp as the actual web application, and not as a regular directory.
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