How to create a seamless pattern from a seamless tile?

[Acorn]

The base tile that you used must have been changed by the website I used to share the image. If you take a look at the last picture that I posted you can see that inside the large square, there are no lines.
https://ibb.co/mB0byVM
Thank you, guys!
I'll read all the posts again and try to figure out what I should do!
I knew that snapping the base tiles could work but I was trying to use a feature that's built-in (the repeating pattern option).

I tried your tile again and it was clean without the edging.

Here is my approach for 1x1, 3x3, 10x10, 20x20: Seamlessly.xar

Acorn