Unable to connect to square

I've been trying for quite a while to get square set up on opencart. Trying to create a webhook results in this message in the square dashboard:

Your webhook for oc2 was not updated. URL is not valid.

I'm using the webhook URL provided in the opencart square setup, oc2 is the name I gave it (I've tried several) and I've tried just one or two selections and all selections of events. Same error message every time.

Since webhooks looked optional, I tried without it. I get a blank browser window from square, it never returns to the OC dashboard (not sure if it's supposed to) but upon going back and refreshing, the OC dashboard says it's still not connected.

I checked the webserver logs and see Square connecting and the server is returning a 200 (which is what Square wants to see). I'm at a loss as to what's going on here. Anyone have any suggestions?

OC Version: 4.0.2.3
Square extension ver: 4.0.5
Square API Version: 2022-02-16 (I've tried a few of these too)
Fresh OC install.
PHP 8.3.10 also tried 7.4.33
I'm in Sandbox mode with this.

Thanks!
Vince.

An update, I did finally create the webhook but I still cannot connect OC to square.