Module Works OK if manually-invoked; Not OK if cron-invoked (environment variables, etc?)

[LEOPARDhost]

G'day,

We've inherited a project with a very long-standing issue, which we believe comes down to the different environments when executing requests inside WHMCS and when the same requests are made via Cron. WHMCS Support were not particularly helpful, and have said "raise a community thread" - though I believe we're on the right track now that it relates somehow to the difference in environments for these 2 invocation methods.

The issue is here, and the latest comment summarises our workings - and why we believe it could be to do with these differences:
https://github.com/LEOPARD-host/BPAY-for-WHMCS/issues/1

There is no problem when the Invoices are downloaded manually, or emailed manually, it's only when the Cron handles this that they're blank.

Although there's mention in the issue of others having fixed this, in a very anti-open-source manner they've consistently refused to contribute code.

We've looked into engaging a developer to assist, but many seem to hate WHMCS, so we're asking here to see if anyone has any wisdom/insight to share!

Primary function of module: To add a "BPAY" payment info image into different WHMCS pages, as well as injecting this into Invoice/Quote PDF files (issue here via-cron only)
Issue we're asking about: Why the PDF injection works OK when invoked by-admin or by-customer, but never works when this is handled by-cron (environment differences?)

Many thanks in advance, it'd be great to make further headway here and ensure it's something we're aware of moving forward. 😊

Cheers,
LEOPARD.host