Allow provider to add services for itself. You need to download these files. form.json you need to import with JetFormBuilder. snippet.json - with code snippets plugin

form.json

{"post_title":"Apply to service","post_content":"<!-- wp:jet-forms\/hidden-field {\"name\":\"provider_id\"} \/-->\n\n<!-- wp:jet-forms\/select-field {\"field_options_from\":\"posts\",\"field_options_post_type\":\"services\",\"name\":\"service_id\"} \/-->\n\n<!-- wp:jet-forms\/submit-field \/-->","meta_input":{"_gspb_post_css":"","_jf_actions":"[{\"id\":3775,\"settings\":{\"send_email\":{\"subject\":\"New order on website\",\"content\":\"Hi admin!\\n\\nThere are new order on your website.\\n\\nOrder details:\\n- Post ID: %post_id%\"},\"call_hook\":{\"hook_name\":\"apply-to-service\"}},\"type\":\"call_hook\",\"conditions\":[],\"events\":[]}]"}}

snippet.json

{"generator":"Code Snippets v3.3.0","date_created":"2023-10-25 10:50","snippets":[{"name":"Apply To Service","scope":"global","code":"add_action( 'jet-form-builder\/custom-action\/apply-to-service', function( $request ) {\n\t\n\t$provider_id = isset( $request['provider_id'] ) ? $request['provider_id'] : false;\n\t$service_id  = isset( $request['service_id'] ) ? $request['service_id'] : false;\n\t\n\tif ( ! $provider_id || ! $service_id ) {\n\t\treturn;\n\t}\n\t\n\t$services_cpt  = \\JET_APB\\Plugin::instance()->settings->get( 'services_cpt' );\n\t$providers_cpt = \\JET_APB\\Plugin::instance()->settings->get( 'providers_cpt' );\n\t$meta_key      = jet_engine()->relations->legacy->get_relation_hash( $services_cpt, $providers_cpt );\n\t\t\n\t$related_posts = jet_engine()->relations->legacy->get_related_posts([\n\t\t'hash'    => $meta_key,\n\t\t'type'    => 'many_to_many',\n\t\t'post_id' => $provider_id,\n\t]);\n\t\n\tif ( empty( $related_posts ) ) {\n\t\t$related_posts = [];\n\t}\n\t\n\t$related_posts[] = $service_id;\n\t\n\tjet_engine()->relations->legacy->process_meta( false, $provider_id, $meta_key, array_unique( $related_posts ) );\n\t\n} );","priority":"10"}]}