Why isn't my iPhone receiving power?

I recently replaced a customers’ iPhone X Screen. Everything went as expected during the repair and there were no issues.. until I tried to turn the phone on.

I unplugged the battery before the repair. All connectors are seated correctly and there aren’t any visible issues. The pins on the connectors are just fine, but I can not get power to the phone!

I tried hard restarting the phone, plugging it into a computer, and letting it charge for awhile to no avail.

There is just no power to the phone at all. What can I do? Did I miss something?