What does 'You have reached the subscription quota limit' mean?

This message appears when I try to stake my coins on Binance in locked staking. I know that there's a limited slot for staking in general which is why sometimes the option to stake is 'sold out', but I seem to have a problem staking a coin even when a product isn't 'sold out', and what's stopping me from staking is apparently that I 'have reached the subscription quota limit'....what does it mean?