We studied the magnetoresistance (MR) of polycrystal Bi₂Te₂Se topological insulator (TI) microwires contacted with superconducting In₂Bi leads. Bi₂Te₂Se has a simple band structure with a single Dirac cone on the surface and a large non-trivial bulk gap of 300 meV. To study the TI/SC interface, the Bi₂Te₂Se glass-coated microwire with a diameter of d = 17 µm was connected to copper leads on one side using superconducting alloy In₂Bi (T_c = 5.6 K), and on the other side using gallium. The topologically nontrivial 3D superconductor (SC) In₂Bi has proximity-induced superconductivity of topological surface states. To eliminate conventional contribution to superconductivity from the bulk, the resulting edge states of the TI/SC contact area were studied in magnetic fields above H_c2 in In₂Bi. The h/2e oscillations of magnetoresistance (MR) in longitudinal and transverse magnetic fields (up to 1 T) at the TI/SC interface were observed at various temperatures (4.2 k–1.5 K). To explain the observed oscillations, we used magnetic flux quantization, which requires a multiply connected geometry where flux can penetrate into normal regions surrounded by a superconductor. The effective width of the closed superconducting area of the TI/SC interface is determined to be 15 nm from an analysis of FFT spectra and the beats of the MR oscillations for two different directions of magnetic field.