Having some issues with v1.0.1 ... 2 different sites, both fresh plugin installs as well as 1 upgrade, which is unaffected & without error is (Zen 1.5.8; PHP 7.4.33; bootstrap 3.5.2; OPC 2.4.5)

#1 Zen 1.5.8; PHP 7.4.33; bootstrap 3.5.0; OPC 2.4.5
#2 Zen 1.5.8; PHP 7.4.33; bootstrap 3.5.0; OPC 2.4.5

Logs
[14-Feb-2024 15:23:38 UTC] Request URI: /XXX/index.php?cmd=modules&set=payment&module=paypalr, IP address: 000.000.000.000
#1 paypaldp->__construct() called at [/home/XXXX/public_html/XXX/modules.php:187]
#2 require(/home/XXXX/public_html/XXX/modules.php) called at [/home/XXXX/public_html/XXX/index.php:11]
--> PHP Warning: Use of undefined constant MODULE_PAYMENT_PAYPALDP_DEBUGGING - assumed 'MODULE_PAYMENT_PAYPALDP_DEBUGGING' (this will throw an Error in a future version of PHP) in /home/XXXX/public_html/includes/modules/payment/paypaldp.php on line 268.

[14-Feb-2024 15:23:38 UTC] Request URI: /XXX/index.php?cmd=modules&set=payment&module=paypalr, IP address: 000.000.000.000
#1 paypaldp->__construct() called at [/home/XXXX/public_html/XXX/modules.php:187]
#2 require(/home/XXXX/public_html/XXX/modules.php) called at [/home/XXXX/public_html/XXX/index.php:11]
--> PHP Warning: Use of undefined constant MODULE_PAYMENT_PAYPALDP_DEBUGGING - assumed 'MODULE_PAYMENT_PAYPALDP_DEBUGGING' (this will throw an Error in a future version of PHP) in /home/XXXX/public_html/includes/modules/payment/paypaldp.php on line 268.

[14-Feb-2024 15:23:38 UTC] Request URI: /XXX/index.php?cmd=modules&set=payment&module=paypalr, IP address: 000.000.000.000
#1 paypaldp->__construct() called at [/home/XXXX/public_html/XXX/modules.php:187]
#2 require(/home/XXXX/public_html/XXX/modules.php) called at [/home/XXXX/public_html/XXX/index.php:11]
--> PHP Warning: Use of undefined constant MODULE_PAYMENT_PAYPALDP_DEBUGGING - assumed 'MODULE_PAYMENT_PAYPALDP_DEBUGGING' (this will throw an Error in a future version of PHP) in /home/XXXX/public_html/includes/modules/payment/paypaldp.php on line 282.

[14-Feb-2024 15:23:38 UTC] Request URI: /XXX/index.php?cmd=modules&set=payment&module=paypalr, IP address: 000.000.000.000
#1 paypaldp->__construct() called at [/home/XXXX/public_html/XXX/modules.php:187]
#2 require(/home/XXXX/public_html/XXX/modules.php) called at [/home/XXXX/public_html/XXX/index.php:11]
--> PHP Warning: Use of undefined constant MODULE_PAYMENT_PAYPALDP_DEBUGGING - assumed 'MODULE_PAYMENT_PAYPALDP_DEBUGGING' (this will throw an Error in a future version of PHP) in /home/XXXX/public_html/includes/modules/payment/paypaldp.php on line 282.

[14-Feb-2024 15:23:38 UTC] Request URI: /XXX/index.php?cmd=modules&set=payment&module=paypalr, IP address: 000.000.000.000
#1 paypaldp->__construct() called at [/home/XXXX/public_html/XXX/modules.php:187]
#2 require(/home/XXXX/public_html/XXX/modules.php) called at [/home/XXXX/public_html/XXX/index.php:11]
--> PHP Warning: Use of undefined constant MODULE_PAYMENT_PAYPALDP_DEBUGGING - assumed 'MODULE_PAYMENT_PAYPALDP_DEBUGGING' (this will throw an Error in a future version of PHP) in /home/XXXX/public_html/includes/modules/payment/paypaldp.php on line 283.

[14-Feb-2024 15:23:38 UTC] Request URI: /XXX/index.php?cmd=modules&set=payment&module=paypalr, IP address: 000.000.000.000
#1 paypaldp->__construct() called at [/home/XXXX/public_html/XXX/modules.php:187]
#2 require(/home/XXXX/public_html/XXX/modules.php) called at [/home/XXXX/public_html/XXX/index.php:11]
--> PHP Warning: Use of undefined constant MODULE_PAYMENT_PAYPALDP_DEBUGGING - assumed 'MODULE_PAYMENT_PAYPALDP_DEBUGGING' (this will throw an Error in a future version of PHP) in /home/XXXX/public_html/includes/modules/payment/paypaldp.php on line 283.

[14-Feb-2024 15:23:38 UTC] Request URI: /XXX/index.php?cmd=modules&set=payment&module=paypalr, IP address: 000.000.000.000
#1 paypaldp->__construct() called at [/home/XXXX/public_html/XXX/modules.php:187]
#2 require(/home/XXXX/public_html/XXX/modules.php) called at [/home/XXXX/public_html/XXX/index.php:11]
--> PHP Warning: Use of undefined constant MODULE_PAYMENT_PAYPALDP_DEBUGGING - assumed 'MODULE_PAYMENT_PAYPALDP_DEBUGGING' (this will throw an Error in a future version of PHP) in /home/XXXX/public_html/includes/modules/payment/paypaldp.php on line 283.
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2024-02-14 15:08:11: (checkout_one) validateCredentials: Checking (1).
TokenCache::clear, clearing cached token.
The curlPost (v1/oauth2/token) request was successful (200).
{
"token_type": "Bearer",
"expires_in": 32007
}
TokenCache::save, saving access-token; valid for 32007 seconds.

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2024-02-14 15:08:18: (checkout_one) validateCredentials: Checking (1).
TokenCache::get, using saved access-token; expires in 32000 seconds.

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2024-02-14 15:08:18: (checkout_one_confirmation) validateCredentials: Checking (1).
TokenCache::get, using saved access-token; expires in 32000 seconds.

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2024-02-14 15:08:18: (checkout_one_confirmation) pre_confirmation_check starts ...
We are unable to process your PayPal Checkout payment at this time. Please contact us for assistance.
************************************************

2024-02-14 15:09:00: (checkout_one) validateCredentials: Checking (1).
TokenCache::get, using saved access-token; expires in 31958 seconds.

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2024-02-14 15:09:03: (checkout_one) validateCredentials: Checking (1).
TokenCache::get, using saved access-token; expires in 31955 seconds.

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2024-02-14 15:09:03: (checkout_one_confirmation) validateCredentials: Checking (1).
TokenCache::get, using saved access-token; expires in 31955 seconds.

************************************************

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2024-02-14 15:09:03: (checkout_one_confirmation) pre_confirmation_check starts ...
We are unable to process your PayPal Checkout payment at this time. Please contact us for assistance.
************************************************

2024-02-14 15:08:57: () validateCredentials: Checking ().The curlPost (v1/oauth2/token) request was successful (200).
{
"token_type": "Bearer",
"expires_in": 31961
}
************************************************

************************************************

2024-02-14 15:08:57: () validateCredentials: Checking ().The curlPost (v1/oauth2/token) request was successful (200).
{
"token_type": "Bearer",
"expires_in": 31960
}
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I also have an OPC log that looks ok, I can pm you if needed.

Thanks
~Melanie