identifier Microsoft expects for an Ontario sole proprietorship

I’m applying for Microsoft for Startups in Canada on a registered company

I’m blocked at the business verification step. Ontario issued my business a 9-digit Business Identification Number (BIN). However, the Microsoft for Startups portal requires the “Business registration ID number” to be exactly 21 alphanumeric characters.

I don’t want to add zeros or otherwise modify the government-issued registration number because that would make the information inaccurate and could affect my application.

Could you please advise which identifier Microsoft expects, or help me complete the verification manually?

Thank you!