Flat leads to tenancy excuses, difficulties and debts (7)
I believe the answer is:
tedious
'flat' is the definition.
(both can mean dull)
'leads to tenancy excuses difficulties and debts' is the wordplay.
'leads to' suggests taking the first letters.
'and' is a charade indicator (letters next to each other).
'debts' becomes 'IOUs' (promises to pay debts).
The initial letters of 'tenancy excuses difficulties' is 'ted'.
'ted'+'ious'='TEDIOUS'
(Other definitions for tedious that I've seen before include "Wearisome, boring" , "not worth listening to?" , "Outside (anag.)" , "drab" , "Boring, monotonous" .)