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'http-request set-header': failed to parse sample expression <ID> : unknown fetch method 'ID'

Hello Haproxy People,

I am looking at a config that was inherited and appears to have some problems.
Upon restarting haproxy (1.6) the following warnings can be seen in the log:

Startup alert:
‘http-request set-header’: failed to parse sample expression : unknown fetch method ‘ID’

Relevant line form the configuration:
http-request set-header X-Request-Id %[ID]

Could someone point me in the direction of what I should be looking at?
Thank you in advance,

PS:
Interestingly, this results in a warning on version 1.6 but the service restarts with a little bit of delay.
The same config prevents version 1.8 from starting.

At least on haproxy 2.1, use %[unique-id]

eg:
http-request set-header x-request-id %[unique-id]