Gradle unable to resolve dependency

[Erickson29]

so i've been using this bottomdialog on an old project that I developed until last year. A few days ago I needed to update something on the project but I found problem on gradle sync-ing that shows Gradle cannot resolve dependency for this. did I miss something over the year and need to update anything? because I've checked my dependency code and it should be correct according to the userguide on how to add dependency.