Log out and re-log into the native multi-line settings of S7 Edge. S7 Edge has Multi-line settings built into it and you do not need to use DIGITS app for it. If Multi-Line setting does not show up in Settings->Clouds and Accounts (Assuming you have Nougat update installed in S7 Edge). That "perpetual" line waiting for the approval will get vanish magically.
I am confused. Are you using Google Android Message app? That app is not aware of DIGITS capability. But if you are using the stock Samsung Messaging app, then it should work. While you log out from Multi-line settings also uncheck the box to delete existing multi-line data from your device. You might want to clear the App cache of Multi-Line settings from Settings->Applications before you actually relogin. This should resolve your issue. Stale cache data is probably preventing you from sending texts. If the problem persists then please post here. I shall tag some group admin to collect more data from you to debug the issue.