I think the problem is came from assets/js/submission.js
When I submit delete action, This file request to /wp-json/formvibes/v1/submissions with method “DELETE”. But target URL not allow this method.
return function(t){fetch(fvGlobalVar.rest_url+"formvibes/v1/submissions",{method:"DELETE",headers:{Accept:"application/json","Content-Type":"application/json","X-WP-Nonce":fvGlobalVar.nonce},body:JSON.stringify(e)}).then((function(e){return e.json()})).then((function(e){t({type:"ON_DELETE_ENTRIES",payload:"deleted"===e})}))}}
I capture line 14 from : assets/js/submission.js