UPI with ASBA mandatory for retail IPO applications; intermediaries must use listed SCSBs and approved mobile apps. Phase II requires UPI with ASBA as the only payment mechanism for retail investor applications through intermediaries, discontinuing the prior Channel III flow of bid cum application forms to SCSBs for fund blocking. Applications must use SCSBs, mobile apps, and UPI handles listed on the regulator's website; incorrect handles or banks not on the live list risk rejection. Alternate channels remain available for investors whose banks are not live. Intermediaries must retain physical UPI application forms for six months and electronic records for at least three years.