Error 403 when uploading xlsx file of transactions

Hi, I'd like some help with the import function for transactions. I've downloaded the sample file and completed it with my transactions. I want to upload the file but I keep getting the Error 403 Forbidden Access. Is this able to be fixed?

I purchased the OFX Import app and that will upload the transactions from an OFX file, however it does not categorise them correctly (I've set up a number of customised categories and they are all labelled with one of those).

If I am able to upload the XLSX file I'd prefer that to the OFX import. Otherwise, is there a way to bulk edit the transactions once uploaded with OFX to allocate them to the correct categories?

Thanks