This denies access always when initially entering the cloud (7)

'this denies access' is the definition.
(a paywall denies access to online content)

'always when initially entering the cloud' is the wordplay.
'always' becomes 'ay' (archaic term for 'always').
'initially' suggests taking the first letters.
'entering' means one lot of letters goes inside another.
'the cloud' becomes 'pall' (pall can mean a cloud or covering).
The first letter of 'when' is 'w'.
'ay'+'w'='ayw'
'ayw' placed within 'pall' is 'PAYWALL'.