Integration to an existing private POS web service

I’m looking for some guidance or documentation on how I should approach this process. I have a feeling I may have missed something obvious.

I have an appointment scheduling/check out/POS web service i used for my own small business, and I have a clover merchant account. I’m looking for be able to send payment command to my clover device from my web service.

I have created a dev account with clover, and kinda got stuck on the very first thing: OAuth. I got it to work in sandbox mode, with the test merchant, but when I try with my actual merchant account, it doesn’t work and just got stuck at the authentication part. So I’m assuming clover doesn’t initiate the authentication for draft app in sandbox mode.

So I guess I should submit the app for approval? That sounds wrong though because I saw somewhere that integration app won’t be available in app market, and this is just an app for my private use, kinda silly to have to go through this step.

If there is any advice on what I should have done instead, or any pointer, I would appreciate it. Thank you.