Sandbox payments not completing; Opencart 3.0.4.0 and PayPal Checkout Integration V3.0.2

[fgrios]

I am working with a new install of OpenCart 3.0.4.0, currently running under php 7.4 with plans to update to 8.1. I have installed and setup PayPal Checkout Integration V3.0.2 (which came with the 3.0.4.0 installation) in Sandbox mode .  While I am able to pay using PayPal and PayPal-PayLater, neither option ever receives a callback to mark the order complete in the OpenCart Store. I also find no record of payments or attempted payments in the Sandbox. Is there a setting somewhere for that?

[fgrios]

I just completed updating the PayPal Checkout Integration to the latest version (3.1.6). Following this, I placed an order and paid via PayPal. There are no errors in either my PHP or OpenCart error logs. I see the following entries in my raw access logs:

[22/Au[Removed. Phone #s not permitted]+0000] "POST /store/index.php?route=extension/payment/paypal/createOrder HTTP/1.1" 200 59 "https://dev.site.com/store/index.php?route=checkout/checkout" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:129.0) Gecko/20100101 Firefox/129.0"
[22/Au[Removed. Phone #s not permitted]+0000] "POST /store/index.php?route=extension/payment/paypal/approveOrder HTTP/1.1" 200 100 "https://dev.site.com/store/index.php?route=checkout/checkout" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:129.0) Gecko/20100101 Firefox/129.0"
[22/Au[Removed. Phone #s not permitted]+0000] "GET /store/index.php?route=checkout/success HTTP/1.1" 200 6491 "https://dev.site.com/store/index.php?route=checkout/checkout" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:129.0) Gecko/20100101 Firefox/129.0"
[22/Au[Removed. Phone #s not permitted]+0000] "POST /store/index.php?route=extension/payment/paypal[Removed. Phone #s not permitted]00c305 HTTP/1.1" 200 - "-" "PayPal/AUHD–214.0–58610500"

The order still remains marked as pending in the store admin. Under Order History->PayPal Checkout Integration tab, I see this:

When I click on the link, the PayPal sandbox says "We are not able to find this transaction id. Can you please check and try again later."

[Here-to-help]

Did you capture the order ? If only then the transaction ID will be visible in PayPal sandbox account. 

Here's the order:

1. Create Order
2. Buyer will be redirected to approve the order.

3. Capture the order,  once the order is approved.