I haven’t used Buffer in a few years, but not that you can post to Instagram from it …could be a reason to go back to it …even if it’s just for the free version.
Things to remember for posting to Instagram
Make a Virtual Copy
Crop 1:1 for simple square crop
1.91 to 1 for horizontal crop
Save as jpeg
Quality 76 percent
Size 1080 length and width
Make a preset
For Vertical use 4×5 crop
You cannot use Buffer for personal Facebook accounts, as Facebook won’t let them so this app would be for FB pages.