It sounds to me like they pre-paid $968,000 and the prepayment has ben exhausted. I found this confusing as well.
At some point Twitter stopped paying their rent and I’m sure there is a clause in the lease that allows the LL to draw down the letter of credit to pay the rent. Twitter also has an obligation the replenish the LOC.
I'm not a financial analyst so take with grain of salt, that's just how I'd heard it discussed in banking.
edit: and I guess the payee's receiving financial institution is also a signatory if those are different entities from the payee! Or at least can be, I'm running into Dunning Kruger so I'll tap out now.