Automation to send attachment not working consistently

NTDSC

I've seen other posts on this issue, but the responses all say that the attachment itself must be the trigger in order for an attachment to be sent with an alert instead of an update request. However, I had another notification set up where the trigger was checking a box, and it would send an alert with a link to the sheet plus the attachment — and I have confirmation that that notification did in fact include the attachment (see screenshot below).

But just now I duplicated that notification and only changed the message text, and it's not including the attachment

Any help would be appreciated!

NTDSC

Update: I figured it out. The attachment is still not the trigger — checking the box is — but for the desired document(s) to be included in the alert, you just have to attach them right before you check the box.

I always thought that it would send every document attached to the row, but it only sends the one attached right before the trigger. For example, the below row has 4 attachments, but I uploaded the PDF and then immediately checked the box, and it went through. Presumably because it's only including "recent updates" — even though that's not really what the alert function necessarily does? Idk. Point is that it finally succeeded.