If a type A or AC is set, you can not perform a DC test because these switches are not suitable.
If you want to carry out the measurement with the 2-pole adapter, an error message will also appear.
For the test with DC, the N conductor is always required as the DC residual current is generated between N and PE. So use the Schuko insert or contact the third wire on the socket of the 2-pole adapter and contact the N conductor.
In networks without N conductor, this test can not be performed.
If you route an N conductor to the RCD and run an additional line from the N output of the RCD to the profit test, you can then carry out the test