Assign subdomain id to the measure

[dokken]

This usually means that you have not used u in your variational form:

@jz97x

problem = NonlinearProblem(F, u, bcs=[bc]

Please see

Failed to successfully call PETSc function 'KSPSolve'. PETSc error code is: 73, Object is in wrong state

You are redefining w_coupled here, meaning that the automatically computed Jacobian is singular. Please remove this definition. Secondly, please note that we cannot run your code as you haven’t provided a mesh.

or provide a minimal reproducible example