Gradle unable to resolve dependency

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.

Start by reproducing the Gradle sync failure using the dependency instructions from the user guide and identify the missing or unresolved dependency details. Check the project’s Gradle dependency configuration and the Android library’s published dependency information. Done means the dependency resolves successfully during Gradle sync.

Written by the indexing model from the issue text.