When you downgrade your plan and there is a message showing that: "You have more than X number of translated words. You'll be able to downgrade to this plan in Y days when your current plan ends", which prevents you from downgrading your plan.
That is because you have reached the translated words limit in your current plan and you have to keep using your current plan until your current billing cycle ends (one billing cycle with 30 days). Then you could downgrade to lower plans.
You activated the Premium plan on June 06, 2020, and started 30 days billing cycle from this day. Then you have reached 1,000,000 translated words limit on June 21. So you have clicked on downgrade to Essential plan after that. You will not be able to downgrade in that time and will see a notice stated that:
"You have more than 1,000,000 translated words. You'll be able to downgrade to this plan in 15 days when your current plan ends".
That means you only could downgrade to Essential plan when your Premium plan ends on July 06, 2020.
Just click on "Remind me", it will remind you on Dashboard when your current plan ends on July 06, 2020. Then you could check and downgrade your plan.
Right on July 6, there will be a pop-up to notice you as below. Please click on "Go to Pricing" to downgrade your plan.
After your plan downgraded on July 6, you'll start a new billing cycle with Essential plan, definitely you already owned more than 400,000 translated words (it means 1,000,000 words you translated before in Premium plan) still be saved in Essential plan. So you cannot translate word anymore but you could use other functions (ex. Edit translation, Media translation, Convert currency, etc) in your Essential plan as long as these features limit are still available.
To understand about what will happen when you downgrade your plan, please refer to this article.
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