Seems 1.5.x is near identical to Arastta file structure and installed easily.
Ended up getting an error when clicking on the edit button for Square.

Fatal error: Call to undefined method Object::load() in /home/xxx/store.com/system/engine/loader.php on line 146

I have a feeling that it's the "system" folder and Arastta has issues with the file structure.

I attached the module if someone wouldn't mind taking a look and see if they think the "system" file structure is wrong for Arastta.

Arastta is forked from OC 2.0.1, as stated in the documentation: https://arastta.org/docs/developers/opencart-compatibility
It will be compatible with quite many extensions for OC 2.0.3.1, and even newer, but not 2.3+ as the folder structure was restructured. Nor is it compatible with 1.5, as it's quite different too.

Looked through each version and run into the same issue with each.
Not sure what to do with the files/folders in the system folder.
I have a feeling because Arastta system is modified, the system folder needs to be modded as well but I don't know enough to figure out where to relocate everything. So I'll have to put this on hold.

Daniel Alfredson wrote:

Looked through each version and run into the same issue with each.

Each as in all from iSense, or what? iSense has some weird restricted stuff sometimes, reinventing the wheels, so maybe try something else. Maybe worth paying for the one from ClearThinking instead: https://www.opencartx.com/square-payment-gateway

Or even pull out the one being included in newer OC's, and simply rewrite it to fit the folder structure of Arastta/OC 2.0.

Yep. isense version. The 1.5 version is the closest to Arastta file structure and I got the furthest with it, but still ended with an error.

I can fix all the files and folders of the newest version but still have the issue of the system folder and not understanding how to adjust it.
No biggy. I'll look at it another day.

You can't use any 1.5 extensions, as already mentioned, unless you know how to recode them - and it's quite much to recode ...
Forget about the iSense and the system folder, not worth it ... pull it from OC core instead as mentioned ...