I’m having exactly the same problem. I’ve been using it fine this morning but it now tells me I need to upgrade if I want to add any additional interactions. 

Hello ​@Mark Sumner & ​@sinholloway 

With our Enterprise plan, you should be able to create slido with unlimited number of polls. 

If you could reach out to us at support@slido.com we’ll be happy to look at it on our end and help you find out what might cause the issues.

Thank you and we’ll await your e-mail. 

Best,