Hello, sunky
For this problem, if rbf can be changed to nn can be coupled normally, then the problem may be the version problem, you can see this post：https://precice.discourse.group/t/openfoam-calculix-rbf-mapping-error-the-rbf-mapping-of-several-nodes-at-the-interface-is-incorrect/1628, I changed the software version, successfully solved this problem, you can try.
Good luck to you
xiangxiang