Originally Posted by
roki
As others have mentioned, I strongly recommend getting a different card for MS purposes. If you want the Ink categories, get a separate Ink card in your own name, using your SSN as a sole prop, not using your actual business/TIN. This could complicate taxes and if the card does get shut down, it could have an adverse effect on the operations of your business.
I wouldn't do Ink for business and a different Ink for MS. You want totally unrelated cards from different banks or other financial entities. If the OP wants to use Ink for MS, then get an additional joint card for the business.
BTW, I hope the OP has some sort of written and signed legal partnership document that details financial and other responsibilities, including how the partner is to use that joint co-signed credit card (not for any personal expenses, only for authorized/appropriate business expenses).