Indisposed in bed when advertised to appear (6)
I believe the answer is:
billed
'advertised to appear' is the definition.
I can't tell whether this defines the answer.
'indisposed in bed' is the wordplay.
'indisposed' becomes 'ill' (similar in meaning).
'in' means one lot of letters goes inside another.
'ill' put into 'bed' is 'BILLED'.
'when' is the link.
Can you help me to learn more?
(Other definitions for billed that I've seen before include "Advertised" , "Listed in a programme; charged" , "Sent an invoice" , "Caressed" .)