@Paul Peacock -

There is virtually no limit on how many people you can invite, but if you are on a paid Miro plan, you would have to pay for each distinct user who was given full edit access to a board (which is needed for creating or updating sticky notes). 

The only alternative would be to use the Anonymous Guest Editor access which is detailed here: https://help.miro.com/hc/en-us/articles/360012524559-Collaboration-with-Anonymous-Guest-Editors

Kiron

Thanks Kiron