What do you mean by "10 payments" in your free option when all the others just say payments?

This means you can only receive 10 payments per month on the Free Plan. Here's a snippet from the guide I'm linking below:

Payment Submissions (monthly) => This is the number of submissions that have payment integrations on them. You can check this guide on how to create a payment/order form. So for example, we have Paypal payment integration on our form, if a user fills out the form, submitted it and successfully completed the payment, then that would be counted as a payment submission. 

Complete guide: Understanding-Your-Account-Usage-Limits

The reason why the FREE Plans says Receive 10 Payments while all the others just say Receive Payments was because there's no 10 monthly limit for paid plans anymore. Their limit would be Bronze = 1000 | Silver = 10000 | Gold = 100000 submissions per month, regardless if it's a normal submission or a submission with payment involved.