Generic function REST API request not working

This returns the expected JSON:

https:// community.company.com/api.ashx/v2/blogs/posts.json

But when I put the ContentId and ContentTypeId of an object returned in that request in the following request, an unexpected error is returned.

https://community.company.com/api.ashx/v2/genericcontent/3bd947f5-5be9-42c8-aa7d-f53eedf30779/f7d226ab-d59f-476c-9d22-4a79e3f0ec07

I can't include the error in this question because when I try to post it, I am blocked with this message: Only known URLs and the following file extensions are allowed: 123, aac, ai, aiff, art, asf, asx, avi, bmp, csd, db, dmg, doc, docx, drw, eml, flac, flv, gif, gz, ics, jpeg, jpg, log, m4a, m4p, m4v, mdb, mdbx, mid, midi, mmv, mov, mp3, mp4, mpg, msg, ogg, pdf, png, pps, ppt, pptx, ps, psd, qt, ram, rar, rm, rtf, sit, sitx, sql, tif, tiff, txt, vcf, vcs, wav, webm, wma, wmv, wpd, wps, xls, xlsx, xml, zip. Please select a valid file or enter a valid URL..

I've triple checked and the order of the ContentId (first) and ContentTypeId (second) in the request, and the values, are correct.

The page the request is trying to get exists on the site.

Is there something I am missing here? Thanks for any help.