Not a DOI

The resolution service at https://doi.org resolves DOIs. You have attempted to resolve core/journals/development-and-psychopathology/issue/2C03ECD0971FAFF137467C9B62D7968A, which is not a DOI.

core/journals/development-and-psychopathology/issue/2C03ECD0971FAFF137467C9B62D7968A may be a Handle (DOIs are a special sort of Handle). If core/journals/development-and-psychopathology/issue/2C03ECD0971FAFF137467C9B62D7968A is a valid Handle you should be able to resolve it at https://hdl.handle.net.