SCCM gives the error Task sequence has failed with the error code 0x800700A1.

It's likely the harddisk to be installed is unformatted and in RAW-format.
RAW-formats are not liked by SCCM, so check that the harddisk is formatted with eg NTFS.

Press F8 at install to open a command prompt and run the commands below.

diskpart
list disk # Lists the disks
select disk 0 # 0 being the disk to setup
clean # Wipes the disk
create partition primary # Creates windows partition
select partition 1
format quick fs=NTFS # Format primary partition
assign letter C # Optional
exit

The command assign letter c may not always work. It's okay to skip it.

Restart the install and it should be a-ok.

 

Source:
https://prajwaldesai.com/task-sequence-has-failed-with-the-error-code-0x800700a1/