Set torsions for atoms in different residues

I am working with a polymer with a non-aminoacidic backbone comprising two subunits, each defined as individual residues. I have already defined the params file for both subunits; however, I am experiencing issues exploring torsions between these connected residues. I am setting the angle movement using pose.conformation().set_torsion_angle(). This function has worked for angles between atoms inside the same subunit. However, when trying to set_torsion_angle() for atoms residing in different residues, I get the following error:

core.kinematics.AtomTree: [ WARNING ] DOF for this torsion angle could not be found in AtomTree. core.conformation.Conformation: set_torsion_angle failed, unable to find dof_id: atomno= 4 rsd= 3 atomno= 1 rsd= 4 atomno= 3 rsd= 4 atomno= 4 rsd= 4

How could I define this DOF in the AtomTree, or is there a way to resolve this issue differently? I am attaching the params files for both subunits.