Call on British monarch by mistake (6)
I believe the answer is:
erring
'call on british monarch by mistake' is the definition.
I can't tell whether this defines the answer.
'call on british monarch' is the wordplay.
'call' becomes 'ring' (telephone call).
'on' says to put letters next to each other.
'british monarch' becomes 'er' (abbreviation for Elizabeth Regina, British Queen. I am not sure about the 'british' bit.).
'ring' put after 'er' is 'ERRING'.
Can you help me to learn more?
(Other definitions for erring that I've seen before include "Being incorrect" , "Making 7 down" , "Going wrong" , "taking wrong direction" , "Sinful" .)