Hi, thank you for the reply.
I am using a standard form created in the WordPress CMS and have also set a default price in the WordPress CMS. I am using the custom amount function to update the price on-the-fly. The form id is hardcoded, I omitted it in my example above deliberately but the line of code is actually…
add_filter( ‘simpay_form_4454_amount’, ‘simpay_custom_amount’ );
As I say the code was working fine in v2.2.0 so any help would be appreciated.