mrconvert: [ERROR] unknown format for image

Hello! I’m new to MRTRIX3, and I’m currently taking the “Introduction to MRtrix” course (Introduction to MRtrix — Andy's Brain Book 1.0 documentation).

In Tutorial #3: Looking at the Data section, I encountered an error after running the following function:

mrconvert sub-CON02_ses-preop_acq-AP_dwi.nii.gz sub-02_dwi.mif -fslgrad sub-CON02_ses-preop_acq-AP_dwi.bvec sub-CON02_ses-preop_acq-AP_dwi.bval

The error message I received is shown in this image:

Could you please provide guidance on what steps I can take to address this issue?

Thank you!