First you will need to log into Monopoly GO!, go to the friends section, click invite (orange button) and copy the link. The link you will need is in this format: e.g. https://mply.io/xxxxxx or https://s.scope.ly/xxxxxx
N.B. on some Android devices you may not have the option to copy the link directly, in which case we suggest you send the link to the Notes app and then copy the link from the Notes app.
Once copied, you can go to Sticker GO! in the bottom right section Profile > Monopoly and paste it into the Monopoly GO! link field.