Trouble registering a service in AGOL

[clt_cabq]

I am trying to register an AGS feature service in AGOL with credentials saved so others accessing the item or maps that include it don't have to log in using their own credentials. Once I flip the switch to save credentials I and hit 'next' I am prompted for my credentials for the service as expected. However, then I am prompted for credentials a second time - but nothing I enter into that second dialogue seems to work. I've tried the AGS Service credentials, my AGOL credentials, even my enterprise login credentials. What am I missing here? I registered this same service with saved credentials in our enterprise Portal with no issues. I've attached screenshots of the two sets of credential prompts I am receiving.

[sxw_eaglegis]

Hi there,

Just to clarify, are you in your ArcGIS Online site and registering a feature service hosted on another ArcGIS Online site? or is the feature service you are trying to add, hosted elsewhere?

It may be something is getting blocked, when you go to register the service, open the developer tab in your browser and see what the request and response is after you click OK.

[clt_cabq]

the feature service I am adding to AGOL is a REST Feature Service published through ArcGIS Server. I'll check the developer tab as you suggest. I can add the service with stored credentials to Portal, and I can add it without stored credentials to AGOL, just can't seem to get it to accept it in AGOL with stored credentials. 

Edit: I just tried this again and it worked with no issues, very bizarre. If you look at my original post, I didn't receive the first of those two credentials prompts this time around, so unsure what changed between then and now. Its possible our network has been funky recently but I'm unsure how that might contribute exactly.