Disable payment methods field when 0 is entered as amount

aleksis/apps/paweljong/frontend/components/event_registration/EventRegistrationForm.vue

@@ -510,7 +510,8 @@ import SecondaryActionButton from "aleksis.core/components/generic/buttons/Secon
                           :hint="$t('paweljong.event_registration.form.steps.financial.fields.payment_method.help_text')"
                           persistent-hint
                           required
-                          :rules="$rules().required.build()"
+                          :disabled="data.payment.amount === 0"
+                          :rules="data.payment.amount === 0 ? [] : $rules().required.build()"
                         ></v-select>
                       </div>
                     </v-col>