When a player signs up for a public match, they will have the option of joining alone or adding their partner (the article on how to do this can be found here). However, if they wish to invite their friends to participate also, they can invite them by sharing the link of the match via WhatsApp or social media platforms.
Managers can also share this link to increase the number of participants (it requires at least a player to be registered). Simply click on Matches, then on the three dots on the right side of the game and Share. It will copy the link, and now you can share in your social media.
To share a link of a match without registered players you have to assign a court in Matches, filter by without Players, click on the reservation and then Add Court/Confirm. It will generate a booking, so you need to filter again by With booking and will be able to see now the 3 dots on the right side to share the link.