The debt is raised using unsecured convertible notes. This gives max flexibility to MSTR and doesn’t restrict its ability to sell BTC if it needs to. If I were Saylor I would not touch the BTC and just convert the notes to equity if I’m not in a cashflow position to redeem.
https://www.microstrategy.com/press/microstrategy-completes-603-million-offering-of-0875-convertible-senior-notes-due-2031_03-19-2024