They claim to be doing FRB, but it looks like what they actually are is insolvent.
A FRB is a bank where deposits exceed liquid liabilities (cash), but do not exceed liquid plus illiquid liabilities (cash + investments).
When deposits exceed liquid and illiquid liabilities you can't operate as an FRB. Because you are insolvent.
But this is all irrelevant, because Tether isn't a bank. Your bank promises that you can withdraw your deposit. Tether does no such thing - it provides withdrawals as a courtesy. If Tether doesn't feel like letting you withdraw, it's not going to let you withdraw.
A FRB is a bank where deposits exceed liquid liabilities (cash), but do not exceed liquid plus illiquid liabilities (cash + investments).
When deposits exceed liquid and illiquid liabilities you can't operate as an FRB. Because you are insolvent.
But this is all irrelevant, because Tether isn't a bank. Your bank promises that you can withdraw your deposit. Tether does no such thing - it provides withdrawals as a courtesy. If Tether doesn't feel like letting you withdraw, it's not going to let you withdraw.