It really should not be as stressful as it is proving for me to be paid for work I'm doing.
An employer wants to pay me for some work, I want to do the work, my Institute/employer is happy to help facilitate, the work won't take me over any working time regulations, and the money is there to pay for the work.
And yet, still quite possible that I'll be faced with a choice between not getting paid and pay with levels of international tax complexity that'll make me physically ill from stress.

