According to developer
Steven Troughton-Smith, Apple will drop support for 32-bit apps with upcoming iOS
11 that means many legacy apps will no longer supports due to which the developer of this app needs to update it to improve its compatibility to run on iOS 11. 
As earlier starting with iOS 10.3, Apple has started alerting and slowly
been cracking down on 32-bit iOS apps, but it will now completely drop support 32
bit apps and may not work with coming iOS 11 this fall.

Apple will drop support for 32-bit apps with upcoming iOS 11 that means many legacy apps will no longer supports due to which the developer of this app needs to update it to improve its compatibility to run on iOS 11.

Smith tweeted Devs:
I’m hearing very clearly iOS 11 won’t have 32-bit app support at all. Update
legacy apps now if you want them to survive past September.

 How to identify 32-bit apps installed on iPhone