In the handler, I think you are missing the suggest.dictionary parameter, which should be set to the name of your suggestion component. In this case, I believe it would should be set to "titleSuggester."
In this sample URL from the documentation, they have a suggest.dictionary field, and our suggester (which is working) also has this field:
according to docs at lucene.apache.org/solr/guide/8_4/suggester.html#
<https://lucene.apache.org/solr/guide/8_4/suggester.html#> that parameter
is optional ( i am supplying it as url param). I guess i have a problem
with JSON payload to create suggester, but in that case api should error