for the time being you can add the missing method is_enabled_jetpack_simple_payments in the file:
jetpack/modules/simple-payments/simple-payments.php
function is_enabled_jetpack_simple_payments() {
/**
* Can be used by plugin authors to disable the conflicting output of Simple Payments.
*
* @since 6.3.0
*
* @param bool True if Simple Payments should be disabled, false otherwise.
*/
if ( apply_filters( 'jetpack_disable_simple_payments', false ) ) {
return false;
}
// For WPCOM sites
if ( defined( 'IS_WPCOM' ) && IS_WPCOM && function_exists( 'has_blog_sticker' ) ) {
$site_id = $this->get_blog_id();
return has_blog_sticker( 'premium-plan', $site_id ) || has_blog_sticker( 'business-plan', $site_id );
}
// For all Jetpack sites
return Jetpack::is_active() && Jetpack::active_plan_supports( 'simple-payments');
}