Issue with pThumb and Amazon S3 media source

[jonleverrier]

I'm trying to;

Get pThumb to compress images from Amazon S3, and save the cached/compressed version back to S3 too.

I'm using the "aws-s3-media-source" package in the MODX repository https://github.com/modxcms/aws-s3-media-source. When I try and use the media source ID in the phpthumbof settings under "S3 Output Media Source", pThumb throws an error;

[2018-06-03 21:17:22] (ERROR @ /home/user/public/project/core/components/phpthumbof/model/phpthumbof.class.php : 89) [pThumb] No such S3 output media source: 5

Is this a bug or have I missed something here - apologies if I have!