Fatal Error shown when adding a post to a workflow

I have tried different versions of the plugin and WP Core but the issue persists. The actual action does happen on the backend. When creating a post and adding it to the workflow it does get added, however, immediately upon submission, a fatal error screen is shown.

Oasis plugin version: 6.2 and 6.3

WordPress Version: 6.1.1 and 6.2

Full error message:

PHP Fatal error: Uncaught TypeError: str_replace(): Argument #3 ($subject) must be of type array|string, stdClass given in /nas/content/live/omsnwhsudev/wp-content/plugins/oasis-workflow/includes/class-ow-email.php:304#012Stack trace:#012#0 /nas/content/live/omsnwhsudev/wp-content/plugins/oasis-workflow/includes/class-ow-email.php(304): str_replace(‘%first_name%’, ‘Benjamin’, Object(stdClass))#012#1 /nas/content/live/omsnwhsudev/wp-content/plugins/oasis-workflow/includes/class-ow-email.php(179): OW_Email->get_step_mail_content(1231, 12, 57, 25349)#012#2 /nas/content/live/omsnwhsudev/wp-content/plugins/oasis-workflow/includes/class-ow-process-flow.php(958): OW_Email->send_step_email(1231)#012#3 /nas/content/live/omsnwhsudev/wp-content/plugins/oasis-workflow/includes/class-ow-process-flow.php(3405): OW_Process_Flow->save_action(Array, ’57’)#012#4 /nas/content/live/omsnwhsudev/wp-content/plugins/oasis-workflow/includes/class-ow-process-flow.php(4432): OW_Process_Flow->submit_post_to_workflow_internal(25349, Array)#012#5 /nas/content/live/omsnwhsudev/wp-content/plugins/oasis-workflow/includes/class-ow-process-flow.php(4379): OW_Process_Flow->submit_post_to_workflow()#012#6 /nas/content/live/omsnwhsudev/wp-includes/class-wp-hook.php(308): OW_Process_Flow->workflow_submit_action(‘https://omsnwhs…’, 25349)#012#7 /nas/content/live/omsnwhsudev/wp-includes/plugin.php(205): WP_Hook->apply_filters(‘https://omsnwhs…’, Array)#012#8 /nas/content/live/omsnwhsudev/wp-admin/includes/post.php(2107): apply_filters(‘redirect_post_l…’, ‘https://omsnwhs…’, 25349)#012#9 /nas/content/live/omsnwhsudev/wp-admin/post.php(234): redirect_post(25349)#012#10 {main}#012 thrown in /nas/content/live/omsnwhsudev/wp-content/plugins/oasis-workflow/includes/class-ow-email.php on line 304