What will happen if we reach the 100 submissions on the free plan?

what is hapenning when we have 100 submissions and if we use free version ? should we pay to allow people to send more messages ?

If you reach the limit, your forms will be temporarily disabled until the next monthly submissions reset. Upgrading is optional. If you don't want to wait for the reset, you may consider upgrading your account to increase your account limits. 

Note that the monthly submission reset is scheduled every first day of each month, at 00 EST.