Shorten & Customize Links
https://dev.bitly.com/docs/tutorials/shorten-customize-links/
Types of short links
（What is a custom link?と共通と思われる）
Short link with a custom back-half
https://bit.ly/newsupdate
Bitly's generic domain, with a customized back-half
Creating Bitly short links
👉Shorten a Link (Bitly API Reference)
Creating custom links
To customize the back-half of a link, you'll perform an additional PATCH call.
これはミスリーディング
Update Custom Bitlink (Bitly API Reference)はうまくいかなかった
Add Custom Bitlink (Bitly API Reference)で作る必要がある