Syberkonda
Are you able to achieve this with developer mode on official Messages from store without using the linked APK? I swear I've seen the very same ACS URL entry somewhere in Dev options
To access dev mode open messages and click the search on top right. Enter the following and press enter when done:
*xyzzy*
Go to main screen of messages, click profile icon top right. You'll now see dev options.
CAREFUL PLAYING WITH SOME SETTINGS IF YOU AREN'T AWARE OF THEM.
It is possible to fill your migrating SMS messages with testing messages with a number 5555550001 going all the way up to 5555559999 so 10,000 texts that will NOT be removed by deleting the app. It will follow you to every other sms app.
Only perform what the support rep mentioned then to disable the developer mode re-enter the same code in the search bar
*xyzzy*
This menu isn't completely dangerous, it's possible to actually enable flags for upcoming features, just perform due diligence before playing with random entries like I did trying to learn about them.