Left: normalized 1D spatial profile (along the slit) of the UV continuum of source A (black solid line and 1σ uncertainty in gray). The PSF profile measured using the reference star at ∼40″ SE of HLock01-LAB is also shown in blue. The UV continuum of source A is compact, but slightly resolved in our spectrum, as well as in the Subaru image and in the high spatial resolution HST image. Middle: OSIRIS/GTC 1D spectrum of source A. The spectrum is characterized by a strong emission in the Lyα line and a very faint continuum (barely detected). Emission in the C IV, He II, and C III] lines is also present, but this appears much fainter (marked with vertical dashed lines). N V 1238,1242 Å is not detected within a 3σ limit of 2.2  ×  10⁻¹⁷ erg s⁻¹ cm⁻². Right panels: Gaussian fits (blue dashed lines) to the spectral profiles of C IV, He II, and C III] (1σ errors in red).