work, where we will also carry out line simulations.

Discussion and conclusions
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This work presents the very first detection of both deuterated forms of amidogen radical in the ISM. From the observations, column densities and deuterium fractionation values have been derived allowing for a direct comparison with the predictions obtained from chemical networks. We have run a parameter-space exploration using our gas-grain chemical code, implementing a two-stage approach to the dynamical evolution of the source. The observed abundances of all , , and isotopic variants could not be simultaneously reproduced with a single set of modelling parameters, thus indicating that the two-stage approach to the core modelling is inadequate for simulating amidogen isotopic chemistry. More insights on this topic would come from additional observations of deuterated amidogen isotopologues. They are, however, partially hampered by the atmospheric opacity. In fact, The most intense transition of , located at 770GHz, is not accessible with the ground-based facilities because of nearby strong water absorption lines. Hence, observations can rely mainly on the $a$-type $N_{Ka,\,Kc} = 1_{\,0,\,1} \leftarrow 0_{\,0,\,0}$ transition around 413GHz. Luckily, spectral coverage at this frequency is supported by the ALMA 8 Band and the new nFLASH receiver of APEX. As 