Upload to Frame.io stall after Media Encoder opens

My sequence won't export to Media Encoder (it's ok to render and to export to without media encoder). In Prem Pro it runs though as if it's sending but then nothing appears in the queue on the Media Encoder.

Doesn't send to Frame.io either (but I imagine this is caused by the same issue.

This used to work (in a previous version) but now doesn't.

Premiere Pro (Beta) Version 24.50 BETA (Build 19)

Mac Mini M1 2020 

16GB memory

MacOS sonoma 14.4.1