I think it depends.  If you are fairly disengaged from the skids.. aren't expected to be caretaking for them providing rides etc.. then being on the app is not going to be particularly helpful.. or relevant.

If you are a major caretaker for your Skids.. and would otherwise have to coordinate with the EX over logistics.. then being on the app would be good.. same as a grandparent who might be providing daycare.. so that the communication for all would be on the app in record.

In my personal experience and reading hundreds of posts here, it's rare that things work out where a SM can be involved at that level. There are cases....just not many. 

As ESMOD said, circumstances may mandate you need access but if you are not involved deeply in the day-to-day with the SKs, I'd say let your DH pass that info on to you.

My approach was disengagement from the start.  I think I've spoken to BM once and seen her a functions maybe another 3 times.

Ideal scenerio is that you are disengaged 100%.

However... If you are an involved SM in the daily tasks (pick ups, drop offs, homework, etc.) then yes, I feel that you should be included and aware of all schedule changes. 

Prior to disengaging, I did the majority of daily tasks for DH and also BM. I would get p!ssed when DH agreed to a schedule change because, at the time, it did directly affect me. Now, I could care less because nothing changes whether SD13 is at our house or not. She hides in her room and I now take on zero reponsibilites for her. So NOW I see it as not my business and stay out of it. 

Depends on your situation though. 

If you are doing CO  transportation , With changing schedules Yes,  you need to be included.  Also if I wasn't included, I wouldn't read or log into the app. Let SO handle it.  I would not be fighting BM on the app. If she doesn't want you on it. Stay off.   If you are down to using an app things are not good now.  Stay away 

Be careful! Once you open Pandora's box and set that precedence, it's hard to undo. 

BM added me to the co-parenting group chat when she met her GF and added her as well. She felt that everyone "needed to be on the same page." That was a total lie and it quickly turned into a nightmare. In reality, BM wanted to another target to abuse and she wanted her GF to have a seat at the parenting table, but knew it would look bad to create a double standard if I wasn't included too. The communication became incredibly toxic and BM felt she could call me out for how I lived my life, whether SS was here or not. It quickly became less about co-parenting and more about creating drama with me and DH. And soon enough, GF felt bold enough to start engaging in the drama too.

I removed myself from the chat in 2019 and have had no direct contact with BM or GF since, outside of a "hello" when they come to pick SS12 up. I fully regret getting involved in that communication at all. I still have a seat at the co-parenting table if I want, but my seat goes through DH. Him and I consult on what works best for our household and he and BM discuss directly. I strictly function behind the scenes now and prefer it that way. DH will not communicate with GF directly. GF still messages him from time to time, trying to coparent with him, and he ignores it, only responding to BM if it requires a response. In my situation, communication really does need to be between BM and DH, even though BM and GF are making the decisions. 

Include lawyers and the Judge.  Particularly if one side or the other is toxic.

When I was doing the step parent thing....I had two rules for myself 

1. Unless I'm getting a cut of some child support money then the less work I had to do the better 
2. I'd rather be involved behind the scenes because these jealous breeders raise hell simply seeing the new wife's name on anything so as long as they thing everything is the dad's idea then it's smoother sailing. 

NOPE, do not do it.

Keep it bio mom and bio dad. 

IF there is a true emergency---call Dh's lawyer. They will know what to do.

Nope, nope, nope. Not your kid. Not your responsibility. Let your partner take the load. Anything you try to do will back fire eventually.