As Ally stated, we need to establish If the handbrake acts in the caliper (you’ll know as the cable will attach your the caliper via an arm) or does it have ‘parking brake’ shoes in the inside of the disk/drum assembly.
If it acts on the caliper directly then you may have a caliper issue (not uncommon on this setup) and would require a caliper strip/rebuild or replacement.
If it has drums & shoes then the possibility of shoe adjustment, and/or wear may be the issue.