I just added this same module to my software and have yet to find the proper settings, but if IG is the same as a lot of other social networks, then they will have extremely low limits on DM's to prevent DM spam. Hear is what I do to find my settings. I start out by setting the settings to a ridiculously slow settings until I don't get blocked. When you do that you can start to speed the settings up gradually until you get blocked. Once you get blocked again with the settings your using then decrease the setting again until you don't get blocked. Some sites have a session limitation also, so you may have to log out and then wait a set amount of time for the server to rest and then you will be able to DM again under a new session.
PS: I use a throw away accounts for settings discovery, never my main accounts.