When in live mode I get errror: We encountered an unexpected error processing your payment method. Please try again later.

Here is a typical extract from my Drupal log for a successful payment against Opayo's test system:

Web server log

192.168.25.20 - - [13/Dec/2023:15:38:22 +0000] "POST /commerce_opayo_pi/merchantsessionkey/141/tokenize_and_submit?_wrapper_format=drupal_ajax HTTP/1.1" 200 286 "http://drupal-dev3.ihbristol.com/checkout/141/order_information" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/119.0"
192.168.25.20 - - [13/Dec/2023:15:38:23 +0000] "POST /checkout/141/order_information HTTP/1.1" 303 454 "http://drupal-dev3.ihbristol.com/checkout/141/order_information" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/119.0"
192.168.25.20 - - [13/Dec/2023:15:38:23 +0000] "GET /checkout/141/review HTTP/1.1" 200 47126 "http://drupal-dev3.ihbristol.com/checkout/141/order_information" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/119.0"
192.168.25.20 - - [13/Dec/2023:15:38:28 +0000] "POST /checkout/141/review HTTP/1.1" 303 458 "http://drupal-dev3.ihbristol.com/checkout/141/review" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/119.0"
192.168.25.20 - - [13/Dec/2023:15:38:29 +0000] "GET /checkout/141/payment HTTP/1.1" 302 350 "http://drupal-dev3.ihbristol.com/checkout/141/review" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/119.0"
192.168.25.20 - - [13/Dec/2023:15:38:29 +0000] "GET /checkout/141/threedsecure HTTP/1.1" 200 45414 "http://drupal-dev3.ihbristol.com/checkout/141/review" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/119.0"
192.168.25.20 - - [13/Dec/2023:15:38:40 +0000] "POST /commerce_opayo_pi/3dSecure/141 HTTP/1.1" 200 32759 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/119.0"
192.168.25.20 - - [13/Dec/2023:15:38:41 +0000] "POST /checkout/141/threedsecure HTTP/1.1" 302 334 "http://drupal-dev3.ihbristol.com/checkout/141/threedsecure" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/119.0"
192.168.25.20 - - [13/Dec/2023:15:38:41 +0000] "GET /checkout/141/complete HTTP/1.1" 200 36264 "http://drupal-dev3.ihbristol.com/checkout/141/threedsecure" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/119.0"

Drupal log
(attached)

Assuming you're using the 'own form' setting, things normally start with the browser asking the back-end to ask Opayo for a merchant session key, in the first 'POST /commerce_opayo_pi/merchantsessionkey/141/tokenize_and_submit' (see above).

I'm assuming things get partway through, at least to the point where a transaction is registered with Opayo, so I would expect you to have at least a partial set of log messages matching the ones in the attached log file.

The error does seem to have disappeared for now, I've managed to make a successful payment with different card.